Issued  March  17,  1011. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— Bulletin  132. 

A. p.MELVIN,  Chiepof  Bureau. 


A  BACTERIOLOGICAL  STUDY 
OF   HAM   SOURING. 


BY 


C.  N.  McBRYDE,  M.  D., 

Senior  Bacteriologist,  Biochemic  Division. 


■  WASHINGTON: 

GOVERNMENT   PRINTING   OFFICE, 

1911. 


Issued  March  17,  1911. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN  132. 

A.  D.  MELVIN,  Chief  of  Bureau. 


A  BACTERIOLOGICAL  STUDY 
OF  HAM  SOURING. 


BY 

C.  N.  McBRYDE,  M.  D., 
Senior  Bacteriologist,  Biochemic  Division, 


WASHINGTON: 

GOVERNMENT   PRINTING   OFFICE. 

1911. 


THE  BUREAU  OF  ANIMAL  INDUSTRY. 


Chief:  A.  D.  Melvin. 

Assistant  Chief:  A.  M.  Farrington. 

Chief  Clerk:  Charles  C.  Carroll. 

Animal  Husbandry  Division:  George  M.  Rommel,  chief. 

Biochemic  Division:  M.  Dorset,  chief. 

Dairy  Division:  B.  II.  Rawl,  chief. 

Inspection  Division:  Rice  P.  Steddom,  chief;  R.  A.  Ramsay,  Morris  Wooden,  and 

Albert  E.  Behnke,  associate  chiefs. 
Pathological  Division:  John  R.  Mohler,  chief. 
Quarantine  Division:  Richard  W.  Hickman,  chief. 
Zoological  Division:  B.  H.  Ransom,  chief. 
Experiment  Station:  E.  C.  Schroeder,  superintendent. 
Editor:  James  M.  Pickens. 


LETTER  OF  TRANSMITTAL. 


United  States  Department  of  Agriculture, 

Bureau  of  Animal  Industry, 

Washington,  D.  C,  November  2,  1910. 
Sir:  I  have  the  honor  to  transmit  and  to  recommend  for  pubhca- 
tion  as  a  bulletin  of  this  Bureau  a  paper  entitled  "A  Bacteriological 
Study  of  Ham  Souring,"  by  Dr.  C.  N.  McBryde,  senior  bacteriologist 
in  the  Biochemic  Division  of  this  Bureau. 

The  souring  of  hams  is  a  source  of  considerable  loss  in  the  meat- 
packing industry,  and  the  cause  of  this  trouble  has  heretofore  been 
in  doubt.  Dr.  McBryde's  paper  presents  the  results  of  an  exhaustive 
study  of  the  subject,  from  which  it  appears  that  he  has  succeeded  in 
discovering  the  true  cause  of  the  trouble.  Besides  a  description  of  the 
experimental  work  the  paper  discusses  methods  of  preventing  the 
souring  of  hams  and  the  proper  disposal  of  those  which  have  become 
affected. 

Respectfully,  A.  D.  Melvin, 

Cliief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/bacteriologicalsOOmcbriala 


CONTENTS. 


Page. 

Introductory 7 

Method  of  curing  hams 8 

Definition  of  souring 10 

Classification  of  sour  hams  and  location  of  sour  areas 10 

Method  of  detecting  sour  hams 12 

Theories  in  regard  to  ham  souring 12 

Previous  experimental  work  to  determine  cause  of  ham  souring 13 

The  present  experiments 14 

Media  employed 14 

Method  of  procedure  in  examining  hams 15 

Results  of  examination  of  sour  and  sound  hams 16 

Histological  changes  in  sour  hams 17 

Chemical  analyses  of  sour  and  sound  hams 18 

Bacteriological  examination  of  sour  and  sound  hams 20 

Inoculation  experiments  with  hams 21 

Probable  method  by  which  ham-souring  bacillus  enters  hams 33 

Possibility  of  infection  prior  to  slaughter 33 

Possible  infection  from  pickling  fluids 34 

Experiment  to  show  whether  infection  takes  place  from  the  cur- 
ing pickle 34 

Possible  infection  through  manipulation  or  handling 35 

Infection  from  ham  thermometers 35 

Experiment  to  show  whether  hams  become  infected  from  ham 

thermometers 37 

Infection  from  pumping  needles 41 

Infection  from  billhooks 42 

Biological  and  morphological  characteristics  of  the  ham-souring  bacillus. . .  43 

Conditions  favorable  to  growth 43 

Growth  on  different  culture  media 43 

Morphology 46 

Spore  formation 46 

Resistance  to  heat  and  chemical  agents 47 

Gas  production 47 

Acid  production 48 

Pathogenic  properties 48 

Nature  of  the  bacillus 48 

Prevention  of  ham  souring 50 

General  summary  and  conclusions 53 

Acknowledgments : 55 

5 


ILLUSTRATIONS. 


PLATES. 

Plate  I.  Fig.  1.— Section  of  muscular  tissue  from  sound  ham,  showing  muscle 
fibers  cut  longitudinally;  nuclei  sharply  defined  and  cross  stria- 
tion  distinct.  Fig.  2.— Section  of  muscular  tissue  from  sour  ham, 
showing  muscle  fibers  cut  longitudinally;  nuclei  undergoing  dis- 
integration and  cross  striation  indistinct 16 

II.  Fig.  1.— Section  through  muscular  tissue  of  ham  which  has  under- 
gone natural  or  spontaneous  souring,  showing  distribution  of 
bacilli  between  the  muscle  fibers,  which  are  cut  obliquely.  Fig. 
2.— Section  through  muscular  tissue  of  ham  which  has  undergone 
natural  or  spontaneous  souring,  showing  individual  bacilli  between 
the  muscle  fibers,  which  are  cut  somewhat  obliquely 16 

III.  Section  through  muscular  tissue  of  artificially  soured  ham,  showing 

distribution  of  bacilli  between  the  muscle  fibers,  which  are  shown 
in  cross  section.  Fig.  2.— Section  through  muscular  tissue  of 
artificially  soured  ham,  showing  individual  bacilli  between  the 
muscle  fibers,  which  are  cut  longitudinally 26 

IV.  Glucose  bouillon  culture  in  Smith  fermentation  tube  at  four  days. .        48 

TEXT   FIGURES. 

Fig.  1.  Cross  section  through  body  of  ham,  with  sour  areas  indicated  by  shad- 
ing and  dotted  lines H 

2.  Cross  section  through  body  of  ham  to  show  method  of  sampling  for 

chemical  analysis Ig 

3.  Cross  section  through  body  of  artificially  soured  ham,  showing  sour 

areas  and  points  at  which  cultures  were  taken 25 

4.  Diagrammatic  views  showing  construction  of  ham  thermometer 36 

5.  Ham-souring  bacillus  {Bacillus  putrefadens) ,  grown  on  egg-pork  me- 

dium           4g 

6 


A  BACTERIOLOGICAL  STUDY  OF  HAM  SOURING. 


INTRODUCTORY. 

The  souring  of  hams  is  a  matter  of  considerable  importance  to  those 
engaged  in  the  meat-packing  industry,  and  has  been  the  occa- 
sion of  no  little  worry,  as  in  even  the  best-regulated  packing  estab- 
lishments the  yearly  losses  it  entails  are  considerable.  The  subject 
has  given  rise  to  much  speculation  on  the  part  of  those  engaged  in  the 
curing  of  meats,  as  to  the  cause  of  the  trouble  and  how  it  may  be 
remedied,  and  has  received  considerable  attention  in  a  practical  way, 
but  little  seems  to  have  been  done  in  a  scientific  way  toward  de- 
termining the  cause  and  nature  of  ham  souring. 

In  a  well-regulated  meat-packing  establishment  the  loss  from  ham 
souring  is  usually  figured  at  about  one-tenth  of  1  per  cent  of  the  total 
weight  of  hams  cured.  At  first  thought  this  would  seem  but  a  small 
loss,  but  when  one  reflects  that  in  a  single  large  packing  establishment 
some  3,000,000  hams  are  cured  during  the  year,  the  loss,  when  figured 
out,  is  considerable.  Taking  15  pounds  as  the  average  weight  of  a 
ham,  3,000,000  hams  would  represent  45,000,000  pounds  of  meat. 
Figuring  the  loss  from  souring  on  the  basis  mentioned,  the  amount  of 
meat  condemned  and  destroyed  during  the  year  would  be  45,000 
pounds.  Assuming  that  hams  sell  at  an  average  wholesale  price  of 
15  cents  a  pound,  the  yearly  loss  for  a  single  plant  which  cures 
3,000,000  hams  a  year  would  be  nearly  $7,000. 

While  one-tenth  of  1  per  cent  of  the  total  weight  of  hams  cured 
would  represent  the  loss  from  souring  in  a  well-regulated  establish- 
ment, statistics  obtained  through  Government  meat  inspectors  show 
that  0.25  per  cent  would  more  nearly  represent  the  loss  for  the  entire 
country.  During  the  fiscal  year  from  July  1,  1908,  to  June  30,  1909, 
some  670,000,000  pounds  of  hams  were  placed  in  cure  in  packing 
establishments  subject  to  Government  inspection.  Estimating  the 
loss  from  souring  at  0.25  per  cent,  the  total  amount  of  meat  con- 
demned and  destroyed  as  sour  would  be  1,675,000  pounds.  At  15 
cents  a  pound  the  total  annual  loss  from  ham  souring  in  packing 
houses  subject  to  Government  inspection  would  figure  up  something 
over  a  quarter  of  a  million  of  dollars. 

The  problem  of  ham  souring,  therefore,  is  quite  an  important  one 
from  a  practical  and  financial  standpoint ;  but  aside  from  these  con- 
siderations it  is  also  a  subject  of  considerable  scientific  interest,  and 

7 


8  A  BACTERIOLOGICAL  STUDY   OF   HAM   SOURING. 

in  view  of  the  fact  that  all  sour  meats  are  condemned  under  the  Federal 
regulations  governing  meat  inspection  it  has  seemed  fitting  that 
this  question  should  be  made  the  subject  of  scientific  investigation  on 
the  part  of  the  Bureau  which  is  charged  with  the  administration  of 
tliis  inspection. 

The  investigation  reported  in  this  paper  has  been  conducted  chiefly 
along  bacteriological  lines,  and  has  been  confined  entirely  to  the  wet 
method  of  curing  hams,  as  this  method  is  the  one  generally  used  in 
American  packing  houses. 

METHOD  OF  CURING  HAMS. 

In  order  to  make  clear  certain  points  in  regard  to  the  nature  and 
occurrence  of  ham  souring  and  to  insure  a  better  understanding  of  the 
experiments  which  are  to  be  described  later,  it  would  seem  best  to 
begin  with  a  brief  outhne  of  the  method  of  curing  hams  as  practiced 
in  the  larger  packing  establishments  of  the  country.  This  description 
is  merely  a  general  outline  of  the  method  of  preparing  hams  for  cure 
and  the  method  of  handling  hams  while  in  cure,  and  deals  cliiefly  with 
those  points  that  bear  on  the  question  of  souring. 

After  the  slaughtered  animal  has  been  cleaned,  scraped,  eviscer- 
ated, washed,  and  split  down  the  middle,  the  carcass  is  usually 
allowed  to  hang  for  an  hour  or  so  in  a  large  room  open  to  the  out- 
side air,  known  as  the  "hanging  floor."  This  is  done  with  a  view  to 
getting  rid  of  a  certain  amount  of  the  body  heat  before  the  carcass  is 
run  into  the  chill  rooms,  and  effects  a  saving  in  refrigeration. 

The  carcasses  are  next  run  into  "coolers"  or  chill  rooms,  and  sub- 
jected to  refrigeration  with  a  view  to  ridding  them  entirely  of  their 
body  heat.  The  coolers  are  large  rooms  fitted  with  brine  pipes  and 
capable  of  accommodating  several  hundred  carcasses.  The  tempera- 
ture of  the  coolers  when  the  carcasses  are  run  in  is  about  32°  F. 
When  filled,  the  temperature  of  the  cooler  rises  to  about  45°  F.,  owing 
to  the  heat  given  off  from  the  carcasses.  The  temperature  is  then 
gradually  reduced  to  28  or  30°  F.  Hog  carcasses  are  left  in  the  coolers 
as  a  rule  for  forty-eight  hours,  at  the  end  of  which  time  they  are  stiff 
and  firm,  but  not  frozen.  The  temperature  of  the  chill  rooms  is 
always  carefully  watched,  thermometer  readings  being  made  every 
few  hours  and  duly  recorded.  The  temperature  of  the  carcasses  is 
always  tested  when  they  leave  the  chill  room.  In  those  plants  pro- 
vided with  a  hanging  floor,  a  certain  number  of  the  carcasses  are  also 
tested  before  they  are  sent  to  the  chill  rooms  in  order  to  determine 
the  amount  of  heat  lost  on  the  hanging  floor. 

The  carcasses  are  tested  by  means  of  an  especially  constructed 
thermometer,  known  as  a  "ham  thermometer,"  which  has  a  pointed 
metal  protector  so  that  it  can  be  thrust  into  the  body  of  the  ham. 
(See  fig.  4.)     The  ham  has  been  rightly  selected  as  the  proper  portion 


METHOD  OF   CUBING  HAMS.  9 

of  the  carcass  at  which  to  take  the  temperature,  as  it  constitutes  the 
largest  mass  of  muscular  tissue  in  the  carcass  and  holds  the  body  heat 
longer  than  any  other  portion.  In  taking  the  temperature,  the  ther- 
mometer is  thrust  deep  into  the  body  of  the  ham  so  that  the  point  of 
the  thermometer  rests  alongside  or  a  little  behind  the  upper  portion 
of  the  femur  or  middle  bone,  the  latter  being  used  as  a  guide  in  intro- 
ducing the  thermometer.  A  certain  number  of  the  carcasses  from 
each  cooler  are  tested  in  this  way  as  a  check  on  the  refrigeration.  The 
inside  temperature  of  the  hams  when  they  leave  the  chill  rooms 
should  be  about  34°  F. 

The  carcasses  are  next  cut  up  and  the  hams  trimmed  for  pickling. 
In  some  houses  the  hams  are  given  an  additional  chilling  of  48  hours 
after  they  are  cut  from  the  carcasses,  but  this  is  not  done  as  a  rule, 
nor  does  it  seem  to  be  necessary. 

The  hams  are  now  sent  to  the  pickling  rooms,  or  ''sweet  pickle 
department,"  as  this  branch  of  the  packing  house  is  designated,  and 
here  a  certain  number  are  again  tested  with  a  thermometer,  as  de- 
scribed above.  This  test  is  carried  out  by  the  foreman  in  charge  of  the 
sweet  pickle  department  in  order  that  he  may  satisfy  himself  that  the 
hams  are  properly  chilled  before  they  go  into  the  pickle  and  as  an 
additional  check  on  the  refrigeration. 

The  hams  are  now  ready  to  be  "pumped,"  and  this  pumping,  as 
will  be  shown  later,  constitutes  an  important  step  in  a  successful  cure. 
Pumping  consists  in  forcing  a  strong  brine  solution  containing  salt- 
peter into  the  muscular  tissues  of  the  ham,  and  is  accomplished  by 
means  of  a  large,  hollow,  fenestrated  needle  connected  by  means  of  a 
rubber  hose  with  a  powerful  hand  pump.  The  needle  is  introduced 
along  the  bone,  the  latter  being  used  as  a  guide. 

In  all  of  the  larger  packing  establishments  two  general  metliods  of 
curing  hams  are  followed,  the  two  methods  being  designated  as  the 
''  fancy  "  or  "  mild  cure  "  and  the  "  regular  cure,"  the  term  "  cure  " 
being  used  to  designate  the  curing  period.  Various  trade  names  are 
given  by  the  different  packing  establishments  to  the  hams  cured  by 
these  methods.  In  the  fancy  cure  the  hams  are  pumped  in  the  shank 
only,  whereas  in  the  regular  cure  they  are  pumped  in  both  body  and 
shank.  The  same  pumping  pickle  is  generally  used  for  the  two  cures. 
It  is  a  significant  fact  that  the  greater  proportion  of  the  "sours"  are 
found  among  the  fancy  or  mild  cure  hams.  This  point  will  be  discussed 
farther  on  in  connection  with  some  experiments  to  be  described  later. 

Tlie  actual  curing  is  usually  carried  out  in  large  vats  wliich  hold 
about  1,400  pounds  of  meat  or  some  hundred  hams.  The  hams  are 
packed  in  the  vats  in  layers  and  are  entirely  covered  with  the  pickling 
solution  or  brine.  A  certain  proportion  is  always  observed  between 
the  weight  of  the  meat  and  the  amount  of  the  solution.  The  pickling 
solution,  or  ''pickle,"  as  it  is  termed,  is  a  brine  solution  containing 
70973°— Bull.  132—11 2 


10  A  BACTERIOLOGICAL  STUDY  OF   HAM  SOURING. 

saltpeter  and  sugar.  The  composition  of  the  pickle  varies  somewhat 
with  the  different  packing  establishments.  The  fancy-cure  hams  are 
usually  cured  in  a  milder  pickle,  that  is,  one  that  contains  less  salt 
and  saltpeter  than  the  pickle  used  in  the  regular  cure,  although  in 
some  packing  establishments  the  same  curing  pickle  is  used  for  the 
two  cures,  the  only  difference  being  the  additional  pumping  given  the 
regular-cure  hams.  The  pickling  rooms,  or  "cellars,"  as  they  are 
called,  are  held  at  a  temperature  of  34°  to  36°  F.,  and  the  pickling 
solutions  are  always  chilled  to  this  temperature  before  being  used. 

The  hams  are  allowed  to  remain  in  cure  for  about  60  days,  and 
during  this  time  are  ''overhauled"  several  times.  Overhauling  con- 
sists in  throwing  the  hams  from  the  vat  in  which  they  are  packed  into 
a  neighboring  empty  vat,  and  then  transferring  the  pickle  to  the  new 
vat.  The  pickle  is  not  changed,  and  the  same  pickle  follows  the  hams 
tlirough  the  entire  curing  process.  The  object  in  overhaulmg  is  to 
stir  up  the  pickle  and  expose  fresh  surfaces  of  the  meat  to  its  action. 

Hams  are  also  cured  in  tierces  which  hold  about  300  pounds  of 
meat.  In  the  tierce  cure,  the  hams  are  packed  in  the  tierces,  the 
Jatter  are  then  headed  up,  the  pickling  solution  is  next  run  in  through 
the  bunghole,  so  as  to  fill  the  tierce  entirely,  and  a  wooden  stopper 
is  finally  driven  into  the  bunghole.  The  tierces  are  rolled  back  and 
forth  across  the  floor  on  dates  corresponding  to  the  dates  of  over- 
hauling in  the  vat  cure.  The  object  of  the  rolling  is  to  stir  up  the 
pickle,  and  in  this  way  it  corresponds  to  overhauling  in  the  vat  cure. 

DEFINITION  OF  SOUHING. 

To  the  meat  inspector,  a  sour  ham  is  one  which  has  a  tainted  or 
"off"  odor,  that  is,  any  odor  wliich  deviates  from  the  normal.  The 
odor  may  be  very  slight,  so  slight  that  at  times  only  the  trained  meat 
inspector  can  detect  it.  When  slight,  the  odor  is  elusive  and  hard  to 
define,  but  wdien  pronounced  it  has  a  distinctly  putrefactive  quality. 
When  not  very  pronounced,  the  odor  possesses,  as  a  rule,  a  slightly 
sour  quahty,  chemically  speaking,  and  at  times  this  sour  quality  may 
be  quite  marked;  hence  the  term  "sour  ham,"  or  "sour"  has  orig- 
inated. In  a  badly  soured  ham — using  the  term  "sour"  in  the 
packing-house  sense  to  denote  any  ham  that  is  tainted — the  odor 
loses  tliis  sour  quality  and  becomes  distinctly  putrefactive  in  nature. 

CLASSIFICATION  OF  SOTJB  HAMS  AND  LOCATION  OF  SOUB  ABEAS. 

Sour  hams  are  classed  as  "shank  sours"  and  "body  sours,"  accord- 
ing to  the  location  of  the  souring,  and  these  may  be  "light"  or 
"heavy."  When  the  souring  is  very  pronounced,  the  ham  is  termed 
a  "stinker." 

Souring  appears  to  start,  as  a  rule,  around  the  stifle  joint  (femoro- 
tibial  articulation),  and  extends  upward  into  the  body  of  the  ham. 


LOCATION    OF   SOUR  AREAS  IN   HAMS. 


11 


In  quite  a  large  proportion  of  the  hams  which  are  sour  in  the  body — 
probably  from  40  to  50  per  cent — the  souring  extends  through  to  the 
bone  marrow  of  the  femur  or  middle  bone,  and  the  sour  odor  is  at 
times  more  pronounced  in  the  bone  marrow  than  in  the  meat.  The 
odor  of  the  bone  marrow,  when  pronounced,  is  strongly  suggestive  of 
a  dissecting-room  odor,  and  is  distinctly  putrefactive  in  quality. 

In  the  case  of  light  body  sours  the  sour  odor  is  confined  to  a  small 
area  immediately  around  the  bone,  and  may  be  so  sHght  that  it  is 
detected  only  with  difficulty.  In  such  hams  the  bone  marrow  is  apt 
to  be  sweet,  and  it  is  not  until  the  souring  becomes  more  extensive 
that  the  bone  marrow  becomes  involved. 


Bands  of  connective 
tissue  and  fat. 


Cut  endc(f 
iFemur. 


Slfinned  surfece. 

Fig.  1. — Cross  section  through  body  of  ham,  with  sour  areas  Indicated  by  shading  and  dotted  lines. 

The  distribution  of  the  sour  area  in  the  body  of  a  well-developed 
sour  is  shown  in  figure  1 . 

In  the  case  of  a  well-developed  body  sour  the  sour  area  is  more 
pronounced  near  the  bone,  as  represented  in  figure  1  by  the  shaded 
area,  and  may  extend  out  into  the  body  of  the  ham  for  a  variable 
distance,  according  to  the  degree  of  souring,  as  represented  by  the 
dotted  lines,  gradually  fading  off  toward  the  margins,  where  it  may 
be  imperceptible  or  entirely  wanting. 

In  the  pronounced  sours,  termed  "stinkers,"  the  odor  pervades  the 
entire  ham,  and  is  of  a  distinctly  putrefactive  quality. 

In  shank  sours,  the  souring  is  more  or  less  confined  to  the  shank, 
or  the  region  about  the  tibio-femoral  articulation,  but  may  extend 
upward  into  the  lower  portion  of  the  body  of  the  ham. 


12  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

METHOD  OF  DETECTING  SOUR  HAMS. 

Souring  is  detected  and  located  by  means  of  a  pointed  metal  instru- 
ment known  as  a  "ham  trier/'  which  resembles  a  long,  slightly  flat- 
tened ice  pick.  The  trier  is  thrust  into  the  ham  at  different  points 
along  the  bone,  rapidly  withdrawn,  and  the  odor  which  clings  to  the 
metal  noted.  The  trained  inspector  works  very  rapidly,  and  is 
able  to  detect  even  the  slightest  sour  or  off  odor  which  might  be 
imperceptible  to  one  not  trained  to  the  work.  At  the  end  of  the 
cure  all  hams  are  tested  with  the  trier  under  the  supervision  of 
Government  meat  inspectors. 

Hams  are  also  given  what  is  called  the  "30-day  inspection"  by 
plant  inspectors  during  the  process  of  curing.  An  average  ham 
weighing  from  14  to  16  pounds  requires  about  60  days  to  cure,  and  at 
the  end  of  30  days  a  certain  number  of  hams  in  each  run  are  usually 
tested  to  see  how  the  cure  is  progressing.  If  no  sour  hams  are 
discovered  at  this  inspection  the  packer  knows  that  the  cure  is  pro- 
gressing satisfactorily,  and  moreover  he  feels  sure  that  his  hams  will 
finish  satisfactorily,  for  experience  has  taught  him  that  souring  develops 
within  the  first  four  weeks  of  the  curing  period,  and  if  his  hams  are 
sweet  at  the  end  of  this  time,  he  can  feel  practically  sure  that  no  sours 
will  develop  later  on. 

THEORIES  IN  REGARD  TO  HAM  SOURING. 

The  theories  as  to  the  cause  of  souring  are  many  and  varied.  The 
majority  of  them  are  pure  speculation  and  have  no  foundation  upon 
observed  facts.  A  few  of  these  theories  may  be  enumerated  to  show 
how  wide  and  varied  has  been  the  speculation  upon  this  subject. 

A  theory  which  is  quite  prevalent  among  packing-house  employees 
attributes  souring  to  overheating  of  the  animal  previous  to  slaughter, 
but  tests  were  made  by  driving  hogs  to  the  point  of  exhaustion  just 
prior  to  slaughter  and  curing  the  hams  from  these  animals  in  com- 
parison with  hams  taken  from  animals  which  had  been  rested  prior 
to  slaughter,  with  no  difference  in  the  cured  product;  that  is,  the 
hams  taken  from  overheated  hogs  cured  equally  as  well  as  those 
taken  from  rested  hogs. 

Another  theory  attributes  souring  to  a  diseased  condition  of  the 
meat.  Prior  to  the  enforcement  of  the  Federal  regulations  governing 
meat  inspection  there  might  have  been  some  ground  for  such  a  sup- 
position, but  this  theory  could  not  hold  at  the  present  time,  in  view 
of  the  thorough  and  efficient  inspection  now  in  force,  for  it  can  be 
safely  said  that  no  diseased  meat  now  passes  the  Government  inspec- 
tors, and  therefore  no  diseased  meat  goes  into  cure  in  inspected  houses. 
In  order  to  test  this  theory,  however,  hams  were  secured  from  a 
number  of  condemned  animals  which  show^ed  various  diseased  con- 
ditions, such  as  hog  cholera,  pyemia,  septicemia,  scirrhous  chord,  etc., 
and  these  hams  were  cured  in  comparison  with  hams    taken    from 


THEORIES  IN   REGARD  TO  HAM  SOURING.  13 

normal  hogs.  It  was  found  that  the  hams  taken  from  the  diseased 
hogs  cured  equally  as  well  as  those  taken  from  healthy  hogs.  The 
hams  from  the  diseased  hogs  were  destroyed  after  the  experiment,  as 
the  meat  taken  from  diseased  animals  was  of  course  not  considered 
fit  for  consumption,  the  object  of  the  experiment  being  merely  to 
determine  whether  or  not  souring  is  caused  by  diseased  conditions. 

Another  theory  attributes  souring  to  imperfect  or  too  rapid  chilling 
of  the  meat  before  it  is  put  in  pickle,  and  places  the  blame  upon  the 
refrigeration.  According  to  this  theory,  souring  results  when  the 
meat  is  chilled  too  suddenly,  the  idea  being  that  by  the  rapid  con- 
gealing of  the  juices  of  the  meat  a  coating  is  formed  on  the  outside 
of  the  ham  whereby  the  animal  heat  is  prevented  from  escaping  from 
the  interior,  leaving  the  meat  next  to  the  bone  at  a  higher  tempera- 
ture than  the  outside  of  the  ham. 

In  order  to  test  this  last  theory,  a  number  of  hog  carcasses  were 
run  direct  from  the  killing  floor  to  a  cooler  at  28°  F.  and  a  like 
number  of  carcasses  of  the  same  average  weight  which  had  been 
allowed  to  stand  for  two  hours  at  the  outside  temperature  of 
the  air  (53°  F.)  were  placed  in  the  same  cooler.  The  carcasses 
which  had  hung  for  two  hours  in  the  air  had  lost  an  average  of 
14  degrees  in  temperature  before  going  to  the  cooler.  The  tem- 
perature of  the  cooler  rose  to  29°  F.  after  the  carcasses  were  put 
in,  but  was  soon  reduced  to  28°  F.  and  held  at  this  temperature. 
The  temperatures  of  the  hams  were  taken  at  the  end  of  24  hours,  and 
practically  no  difference  was  found  in  the  inside  temperatures  of  the 
two  lots;  that  is,  the  hams  on  the  hot  carcasses  which  were  subjected 
to  a  sudden  chilling  exhibited  practically  the  same  inside  temperature 
(i.  e.,  next  to  the  bone)  as  those  which  had  cooled  for  two  hours  at 
the  temperature  of  the  air  before  being  placed  in  the  cooler. 

Still  another  theory  attributes  souring  to  lack  of  penetration  of  the 
pickling  fluids,  but  analyses  of  sour  and  sound  hams  do  not  seem  to 
bear  out  this  theory.  The  rate  of  penetration  of  the  pickling  fluids, 
however,  would  seem  to  have  some  bearing  on  the  subject,  and  this 
point  will  be  discussed  later  in  connection  with  some  laboratory 
experiments  on  the  inhibitory  effects  of  sodium  chlorid  and  potas- 
sium nitrate. 

So  much  for  the  more  commonly  accepted  theories  which  have 
been  advanced  to  explain  ham  souring. 

PREVIOUS  EXPERIMENTAL  WORK  TO  DETERMINE  CAUSE  OP 

HAM  SOURING. 

A  review  of  the  literature  reveals  but  one  article  bearing  directly 
on  the  subject  of  the  cause  of  ham  souring. 

In  June,  1908,  Klein*  published  in  the  London  Lancet  an  article 
on  "miscured"  hams.     He  describes  a  miscured  ham  as  one  which 

I  Klein,  E.    On  the  nature  and  causes  of  taint  in  miscured  hams.    The  Lancet,  vol.  174,  London,  June 
27, 1908. 


14  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOUfilNG. 

has  a  distinctly  putrid  smell,  and  the  tainted  areas  he  describes  as 
varying  in  color  from  a  dirty  gray  to  a  dirty  green,  the  muscular 
tissues  in  the  strongly  tainted  areas  being  swollen  and  soft,  or  jelly-like. 
From  such  hams  he  isolated  a  large  nonmotile,  nonspore-bearing, 
anaerobic  bacillus  which  he  calls  Bacillus  foedans.  He  cultivated  the 
organism  on  different  media  and  obtained  from  the  cultures  a  putrid 
odor  resembling  that  of  the  ham  from  which  the  culture  was  obtained, 
but  did  not  attempt  to  produce  tainting  by  injecting  sound  hams 
with  the  bacillus. 

While  there  can  be  little  doubt  that  Klein's  bacillus  was  the  cause 
of  the  tainting  in  those  hams  which  he  examined,  the  proof  would 
certainly  have  been  stronger  had  he  injected  sound  hams  with  cul- 
tures and  thus  proven  that  he  could  reproduce  tainting  experimentally 
by  means  of  his  bacillus.  Klein  examined  only  dry-cured  hams  and 
does  not  state  the  temperature  at  which  they  were  cured.  He  fails 
to  offer  any  explanation  as  to  how  the  bacillus  gained  entrance  into 
the  hams. 

THE  PRESENT  EXPERIMENTS. 
MEDIA    EMPLOYED. 

After  considerable  experimentation  as  to  a  suitable  culture  medium 
for  the  bacteriological  study  of  sour  hams,  a  modification  of  the  "egg- 
meat  mixture"  used  by  Rettger^  in  his  studies  on  putrefaction  was 
found  to  be  the  most  satisfactory.  This  medium,  which  consists  of 
chopped  meat  and  egg  albumen,  furnishes  an  excellent  medium  for 
the  growth  of  putrefactive  organisms  which  rapidly  break  down  the 
proteids  of  the  meat,  giving  rise  to  the  characteristic  odors  of  putrid 
decomposition.  Rettger  used  chopped  beef  and  egg  albumen,  but  for 
the  present  work  chopped  pork  was  substituted  for  the  beef,  as  afford- 
ing a  more  suitable  medium  for  the  growth  of  organisms  accustomed 
to  growth  in  pork  hams.     The  modified  medium  is  prepared  as  follows : 

A.  One-half  pound  of  lean  pork,  freed  from  excess  of  fat  and 
sinew,  is  finely  chopped  in  a  meat  chopper,  250  cubic  centimeters  of 
water  is  then  added,  the  meat  acids  are  neutralized  with  sodium  car- 
bonate, and  the  mixture  is  heated  in  an  Arnold  sterilizer  for  30 
minutes,  with  occasional  stirring.  It  is  then  set  away  in  a  cold 
place  for  several  hours.  A  small  amount  of  fat  collects  at  the  top  in 
the  form  of  a  fatty  scum,  as  it  is  impossible  to  remove  all  of  the  fat 
from  the  meat  before  it  is  chopped.  The  fatty  scum,  which  hardens 
upon  standing  in  the  cold,  is  now  removed. 

B.  The  whites  of  three  eggs  are  mixed  with  250  cubic  centimeters 
of  water.  The  mixture  is  rendered  neutral  to  phenolphthalein  by 
means  of  dilute  hydrochloric  acid  and  heated  for  30  minutes  in  the 
Arnold  sterilizer,  with  occasional  stirring. 


•  Rettger,  L.  F.    Studies  on  putrefaction.    Journal  of  Biological  Chemistry,  vol.  2, 1906. 


METHOD  OF   EXAMINING  HAMS.  15 

A  and  B  are  now  mixed  and  2.5  grams  (0.5  per  cent)  of  powdered 
calcium  carbonate  added.  The  mixture  is  next  run  into  large  sterile 
test  tubes,  or  sterile  flasks,  and  sterilized  in  an  Arnold  sterilizer  on 
three  successive  days. 

In  addition  to  the  egg-pork  mixture  described  above,  culture  tubes 
of  agar  and  bouillon  prepared  from  pork  instead  of  beef,  with  the 
addition  of  1  per  cent  of  glucose,  were  also  used;  but  the  best  results 
were  obtained  with  the  egg-pork  medium,  as  with  tliis  medium,  the 
early  development  of  sour  or  putrefactive  odors  furnished  a  valuable 
indication  as  to  the  presence  of  organisms  capable  of  producing  sour 
or  putrefactive  changes  in  meat. 

METHOD    OF    PROCEDURE    IN    EXAMINING    HAMS. 

The  hams  were  sectioned  through  the  body,  the  femur,  or  "middle 
bone,"  as  it  is  known  in  packing-house  parlance,  being  cut  at  a  point 
about  1^  or  2  inches  below  its  head.  A  cross  section  of  a  ham  thus 
cut  is  shown  in  figure  1.  After  sectioning,  the  hams  were  subjected 
to  a  microscopical,  bacteriological,  and  chemical  examination  as 
follows : 

Microscopical  examination. — Bits  of  muscular  tissue,  taken  from 
various  points,  were  teased  out  in  salt  solution  and  the  condition  of 
the  muscle  fibers  noted.  Smear  preparations  were  also  made  from 
bits  of  muscular  tissue  and  from  the  bone  marrow,  and  these  were 
stained  and  subjected  to  microscopical  examination.  Portions  of 
the  meat  were  also  hardened  and  cut  into  microscopic  sections,  which 
were  stained  and  mounted  for  histological  and  bacteriological  study. 

Bacteriological  examination. — In  the  bacteriological  examination 
of  sour  hams,  especial  attention  was  directed  to  the  detection  of 
anaerobic  species,  as  it  seemed  reasonable  to  suppose  that  if  the 
changes  taking  place  in  sour  hams  were  due  to  bacteria  these  bacteria 
would  in  all  likehhood  be  anaerobes  (i.  e.,  organisms  which  develop 
in  the  absence  of  oxygen).  This  assumption  was  based  upon  the  fact 
that,  as  a  rule,  souring  begins  in  the  interior  of  the  ham  next  to  the 
bone,  and,  furthermore,  the  hams  are  cured  in  large  vats  where  they 
are  completely  submerged  in  the  pickling  fluids,  so  that  any  bacteria 
which  develop  within  the  bodies  of  the  hams  while  they  are  in  cure 
are  probably  restricted  to  practically  anaerobic  conditions. 

Cultures  were  made  from  the  interiors  of  the  hams  at  various  points 
by  first  searing  the  cut  surface  thoroughly  with  a  heavy  metal  spatula 
and  then  cutting  out,  by  means  of  sterile  scissors  and  forceps,  plugs 
of  meat  about  1  cm.  square.  The  plugs  of  meat  were  then  dropped 
into  tubes  containing  the  egg-pork  medium  and  pushed  down  to  the 
bottom  of  the  tubes,  where  they  were  held  in  place  by  the  chopped 
meat  above;  in  this  way  conditions  favorable  for  the  development 
of  anaerobic  organisms  were  obtained.     In  inoculating  the  pork-agar 


16  A  BACTERIOLOGICAL  STUDY  OF  HAM  SOURING. 

tubes,  the  medium  was  first  boiled  to  expel  any  inclosed  air  and  cooled 
to  43°  to  45°  C;  the  plugs  of  meat  were  then  dropped  into  the  tubes 
and  the  agar  rapidly  solidified  by  plunging  the  tubes  in  cold  water ; 
in  this  way  the  bits  of  meat  were  inclosed  in  the  agar  at  the  bottom 
of  the  tubes,  affording  suitable  conditions  for  anaerobic  growth. 
Aerobic  and  anaerobic  plates  were  also  made  from  the  meat,  and  in 
most  cases  bouillon  tubes  were  also  inoculated.  Cultures  were  always 
taken  from  the  bone  marrow  as  well  as  from  the  meat.  Novy  jars 
were  also  used  for  obtaining  anaerobic  conditions  in  growing  the  cul- 
tures. 

Chemical  examination. — In  order  to  determine  whether  the  souring 
was  connected  with  or  dependent  upon  a  lack  of  penetration  of  the 
pickling  fluids  to  the  interior  of  the  meat,  the  hams  were  further  sub- 
jected to  a  chemical  examination  and  the  content  of  the  meat  in 
sodium  chlorid  and  potassium  nitrate  determined  at  varying  depths. 

RESULTS    OF    EXAMINATION    OF    SOUR    AND    SOUND   HAMS. 

The  sour  hams  examined  were  obtained  from  four  difl'erent  packing 
establishments.  All  of  the  hams  studied  were  "  sweet-pickle  hams " 
which  had  not  been  smoked.  The  sour  hams  selected  for  examination 
were  good  typical  body  sours,  in  which  the  sour  odor  was  well  devel- 
oped, but  not  of  the  very  pronounced  or  putrefactive  type. 

The  sour  odor  in  every  case  was  found  to  be  more  pronounced  next 
to  the  bone,  being  usually  rather  more  pronounced  just  behind  the 
bone,  that  is,  on  the  fat  side  of  the  bone.  The  sour  odor  in  each 
instance  was  confined  to  an  area  of  meat  immediately  surrounding 
the  femur  and  extending  out  through  the  body  of  the  ham  for  a  vari- 
able distance,  as  shown  by  the  dotted  lines  in  figure  1 ,  but  in  no  case 
did  the  sour  odor  extend  all  the  way  to  the  margin  of  the  meat,  nor 
did  it  as  a  rule  extend  below  the  tibio-femoral  articulation,  the  shank 
proper  and  the  bone  marrow  of  the  shank  (i.  e.,  of  the  tibia)  being 
usually  sweet.  The  butt  portion  of  the  hams — that  portion  above 
and  behind  the  hitch  bone  (symphasis  pubis) — was  also  sweet. 

Immediately  after  sectioning,  the  sour  areas,  as  a  rule,  could  be 
readily  distinguished  by  a  difference  in  color.  In  the  freshly  cut  hams 
the  muscular  tissue  near  the  bone,  where  the  sour  odor  was  more 
pronounced,  exhibited  a  slight  but  distinct  grayish  hue,  at  times  hav- 
ing a  slight  greenish  tinge ;  in  other  words,  the  muscular  tissue  in  the 
sour  areas  lacked  the  normal  bright  red  color  of  the  sound  meat  and 
was  distinctly  lighter  in  color  than  the  surro^mding  tissues.  Upon 
exposure  to  air,  however,  the  lighter,  grayish,  sour  areas  tend  to 
assume  a  reddish  hue  and  become  much  less  pronounced  than  in  the 
freshly  cut  ham.  After  the  cut  surface  of  the  ham  has  been  exposed 
to  the  air  for  some  time  it  may  be  difficult  to  distinguish  the  sour 
areas  by  any  difference  in  color. 


BuL.  132,  Bureau  of  Animal  Industry,  U.  S.  Dept.  of  Agriculture. 


Plate  I. 


Fig.  1.— Section  of  Muscular  Tissue  from  Sound  Ham,  Showing 
Muscle  Fibers  Cut  Longitudinally;  Nuclei  Sharply  Defined 
AND  Cross  Striation  Distinct. 

(Pen-and-ink  drawing  made  with  camera  lucida  from  section  stained  with 
hematoxylin  and  eosin  to  show  histological  structure.    X  320.) 


Fig.  2.— Section  of  Muscular  Tissue  from  Sour  Ham,  Showing 
Muscle  Fibers  Cut  Longitudinally;  Nuclei  Undergoing  Disin- 
tegration and  Cross  Striation  Indistinct. 

(Pen-and-ink  drawing  made  with  camera  lucida  from  section  stained  with 
hematoxylin  and  eosin  to  show  histological  structure,     x  320.) 


BuL.  132,  Bureau  of  Animal  Industry,  U.  S.  Dept.  of  Agriculture. 


Plate  II. 


Fig.  1.— Section  Through  Muscular  Tissue  of  Ham  which  has 
Undergone  Natural  or  Spontaneous  Souring,  Showing  Distri- 
bution OF  Bacilli  Between  the  Muscle  Fibers,  which  are  Cut 
Obliquely.  The  Dark  Masses  Between  the  Muscle  Fibers 
Represent  Clumps  of  Bacilli. 

(Pen-and-ink  drawing  made  with  camera  lucida  from  section  stained  by 
the  Gram-Weigert  method  to  show  bacteria,     x  86.) 


Fig.  2.— Section  Through  Muscular  Tissue  of  Ham  which  has 
Undergone  Natural  OR  Spontaneous  Souring,  Showing  Individual 
Bacilli  Between  the  Muscle  Fibers,  which  are  Cut  Somewhat 
Obliquely.  Nuclei  have  lost  Sharp  Outline  and  Cross  Striation 
is  Indistinct. 

(Pen-and-ink  drawing  made  with  camera  Incida  from  section  stained  by  the 
Gram-Weigert  method  to  show  bacteria,     x  320.) 


HISTOLOGICAL  CHANGES  IN   SOUE  HAMS.  17 

In  the  sour  areas  near  the  bone  the  muscular  tissue  was  distinctly 
softer;  that  is,  it  broke  and  "cut  more  readily  than  the  surrounding 
tissues.  This  was  usually  quite  noticeable  in  cutting  out  plugs  of 
the  meat  for  making  cultures.  In  a  ham  which  shows  pronounced 
souring  the  muscular  tissues  in  the  worst  affected  areas  may  become 
quite  soft  and  even  slightly  gelatinous. 

The  sour  areas,  when  tested  with  litmus  paper,  frequently  showed 
a  slight  but  distinct  alkaline  reaction.  When  aqueous  extracts  of 
the  sour  meat,  however,  were  titrated  with  phenolphthalein  they 
were  found  to  be  acid. 

HISTOLOGICAL    CHANGES    IN    SOUR   HAMS. 

In  preparations  made  by  teasing  out  bits  of  the  meat  in  physiolog- 
ical salt  solution,  the  cross  striation  of  the  muscle  fibers  from  the  sour 
areas  was  found  to  be  much  less  distinct  than  in  similar  preparations 
taken  from  sound  portions  of  the  meat  or  from  sound  hams.  At 
times  it  was  found  that  the  muscle  fibers  in  the  sour  areas  had  com- 
pletely lost  their  cross  striae,  but  the  longitudinal  striation  could  still 
be  made  out.  In  cases  where  the  souring  was  pronounced  there  was 
sometimes  complete  loss  of  both  longitudinal  and  cross  striation;  in 
these  cases  the  muscle  fibers  appeared  to  have  undergone  slight  swell- 
ing and  the  protoplasm  exhibited  a  finely  granular  appearance. 

In  stained  sections  of  the  sour' meat  another  striking  change  was 
noticed  in  the  disintegration  of  the  nuclei  of  the  muscle  fibers,  which 
are  at  times  completely  broken  up,  appearing  as  bluish  granular 
masses  in  sections  stained  with  hemotoxylin  and  eosin.  (Compare 
figs.  1  and  2  of  J*l.  I.) 

In  sections  stained  by  the  Gram-Weigert  method  to  show  the  pres- 
ence of  bacteria,  a  large  Gram-staining  bacillus  was  noted  between 
the  muscle  fibers  in  the  connective-tissue  elements  of  the  muscle. 
In  some  of  the  sections  these  bacilli  were  present  in  great  numbers, 
sometimes  in  densely  packed  clumps  or  masses,  while  in  other  sections, 
or  in  other  portions  of  the  same  section,  they  were  only  sparsely  dis- 
tributed between  the  muscle  fibers.  Where  the  bacteria  were  more 
numerous  the  histological  changes  in  the  muscle  fibers,  especially  the 
breaking  down  of  the  nuclei,  were  more  noticeable.  The  intermus- 
cular connective  tissue  had  apparently  furnished  paths  of  least  resist- 
ance along  which  the  organism  followed.  In  Plate  II,  figures  1  and 
2,  the  bacteria  are  shown  between  the  muscle  fibers  under  low  and 
high  power  magnifications. 

In  Plate  II,  figure  1,  under  the  low-power  magnification,  the  bac- 
teria appear  as  dark  clumps  or  bands  between  the  muscle  bundles. 
Under  the  high  power  they  are  shown  following  along  the  sarcolemma 
sheaths  between  the  muscle  fibers. 
70973°— Bull.  132—11 3 


18 


A   BACTERIOLOGICAL  STUDY   OF    HAM   SOURING. 


CHEMICAL    ANALYSES    OF    SOUR    AND    SOUND    HAMS. 

In  order  to  determine  whether  there  was  any  difference  in  regard 
to  the  penetration  of  the  pickling  fluids  in  the  sour  hams  as  compared 
with  sound  hams,  a  series  of  four  sour  hams  were  subjected  to  a 
chemical  examination  in  comparison  with  four  sound  hams.  Ail 
were  sweet-pickle  hams  and  were  obtained  from  the  same  packing 
establishment.  They  were  all  of  the  same  cure  and  the  same  approx- 
imate age  (i.  e.,  length  of  cure)  and  the  same  approximate  weight. 

In  takmg  samples  for  chemical  analysis,  the  following  procedure 
was  adopted:  A  section  about  2^  inches  wide  was  cut  from  the  center 
of  the  body.  The  two  ends  of  this  section  were  then  trimmed  off 
along  the  lines  L-M  and  N-0,  as  shown  in  figure  2.     Beginning  at  the 


SKin. 


Bone. 


Fig.  2.— Cross  section  through  body  of  ham  to  show  method  of  sampUng  for  chemical  analysis.    A,  slice 
below  bone;  B,  bone  slice;  C,  slice  above  bone:  D,  fat  slice. 

skinned  surface,  four  slices.  A,  B,  C,  and  D,  were  then  made,  as  indi- 
cated by  the  dotted  lines.  Slice  B  contained  the  bone  in  each 
instance.  Slice  D  was  practically  all  fat.  Each  slice  was  ground 
separately  in  a  meat  chopper  and  the  sample  thoroughly  mixed  before 
taking  out  portions  for  analysis. 

As  all  of  the  hams  examined  were  mild-cure  hams,  that  is,  had 
been  pumped  in  the  shank  only,  the  pickling  fluids  in  order  to  reach 
the  bodies  of  these  hams  had  to  penetrate  chiefly  from  the  skinned 
surface  of  the  ham,  as  little  if  any  penetration  takes  place  through 
the  thick  skin  of  the  ham. 

The  analyses  ^  shown  in  the  following  tables  therefore  indicate  the 
degree  of  penetration  of  the  pickling  fluids. 

1  These  analyses  were  made  by  Mr.  R.  R.  Henley,  of  the  Biochemic  Division,  Bureau  of  Aolmal 
Industry 


ANALYSES   OF  SOUE  AND  SOUND   HAMS. 
Analyses  of  sour  hanis. 


19 


No. 


Description. 


Slice. 

NaCl. 

Per  cent. 

A 

6.18 

B 

4.83 

C 

3.65 

D 

1.03 

A 

5.34 

B 

3.70 

C 

2.79 

D 

1.12 

A 

5.04 

B 

4.08 

C 

2.72 

D 

1.19 

A 

7.78 

B 

5.31 

C 

4.76 

D 

1.96 

KN03. 


Sour  body. 


.do. 


.do. 


.do. 


Per  cent. 
0.175 
.224 
.299 
.074 
.174 
.150 
.174 
.012 
.125 
.149 
.099 
.048 
.250 
.100 
.200 
.048 


Analyses  of  sound  hams. 


No. 


Description. 


Slice. 

NaCI. 

Per  cent. 

A 

5.80 

B 

4.83 

c; 

3.86 

D 

1.33 

A 

4.94 

B 

4.08 

C 

3.05 

D 

1.56 

A 

5.92 

B 

4.29 

C 

4.12 

D 

2.32 

A 

5.53 

B 

4.89 

C 

4.32 

D 

2.19 

KNO». 


Sound. 


.do. 


.do. 


-do. 


Per  cent. 
0.211 
.188 
.221 
.063 
.197 
.149 
.223 
.059 
.173 
.099 
.139 
.049 
.119 
.079 
.099 
.041 


Taking  an  average  of  the  four  slices  in  each  ham  so  as  to  get  an 
average  for  the  entire  ham,  and  comparing  the  sour  hams  with  the 
sound  hams,  we  have  the  following  comparison: 


NaCI. 


Average  for  4  sour  hams  (entire  ham) per  cent. .  3.  84 

Average  for  4  sound  hams  (entire  ham) do 3.  93 


KNOj. 

0.143 

.131 


These  figures  show  practically  no  difference  between  the  sour  and 
the  sound  hams  as  regards  the  sodium  chlorid  and  potassium  nitrate 
content  of  the  entire  ham. 

If,  now,  we  compare  the  bone  slices — and  these  afford  really  a 
better  basis  for  comparison,  as  in  sour-body  hams  the  souring  is 
always  more  pronounced  around  the  bone — we  have  the  following 
figures : 


NaCl. 


Average  for  4  sour  hams  (bone  slice) per  cent. .  4.  48 

Average  for  4  sound  hams  (bone  slice) do 4.  52 


KNOj. 

0.155 

.129 


Here,  again,  we  find  no  essential  difference  between  the  sour  and 
the  sound  hams,  and  we  must  conclude  from  these  analyses  that 
souring  does  not  depend  upon  or  result  from  a  lack  of  penetration 
of  the  pickling  fluids. 


20  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

It  seems  probable  that  in  mild-cure  hams,  which  are  pumped  in  the 
shank  only,  the  souring  begins  in  the  upper  portion  of  the  shank  and 
extends  upward  along  the  bone  into  the  body  of  the  ham,  and  that 
it  takes  place  before  the  pickling  fluid  has  penetrated  to  the  interior 
of  the  ham.  When  the  pickling  fluid  reaches  the  interior  of  the  ham 
it  tends  to  inhibit  the  souring,  which,  as  will  be  shown  later,  is  due 
to  the  development  of  bacteria  within  the  bodies  of  the  hams.  The 
growth  of  the  bacteria,  however,  within  the  bodies  of  the  hams  and 
the  histological  changes  in  the  muscle  fibers  do  not  seem  to  interfere 
with  the  penetration  of  the  pickling  fluids. 

BACTERIOLOGICAL    EXAMINATION    OF    SOUR    AXD    SOUND    HAMS. 

In  all  of  the  sour  hams  which  were  examined  bacteriologically  a 
large  anaerobic  bacillus  was  found  to  be  constantly  present.  From 
several  of  the  hams  this  bacillus  was  obtained  in  pure  culture ;  that  is, 
it  was  the  only  organism  present  in  cultures  made  from  the  sour 
meat  and  from  the  bone  marrow  of  the  femur.  Such  cultures,  w^hen 
held  at  room  temperature,  gave,  at  three  days,  a  sour-meat  odor 
exactly  resembling  that  obtained  from  sour  hams. 

In  many  of  the  sour  hams  other  bacteria  were  found  in  association 
with  the  anaerobic  bacillus  noted  above.  These  other  bacteria,  how- 
ever, were  not  constant,  being  sometimes  present  and  sometimes 
absent.  Among  the  other  bacteria  noted  in  the  sour  hams,  the 
following  forms  occurred  most  frequently : 

1.  A  nonmotile,  gram-positive  bacillus,  measuring  from  l.o  to  4 
microns  in  length  by  0.5  micron  in  breadth,  sometimes  in  chains  and 
filaments. 

2.  A  small,  nonmotile,  gram-negative  bacillus,  about  the  size  of 
Bacillus  coli  and  usually  in  pairs. 

3.  A  large  micrococcus. 

Sometimes  one  and  sometimes  all  of  these  bacteria  were  present 
in  a  given  ham.  They  were  encountered  most  frequently  in  hams 
which  had  been  pumped  in  both  body  and  shank,  and  were  probably 
ordinary  pickle  bacteria.  They  were  not  strict  anaerobes,  but 
belonged  to  the  class  of  facultative  or  optional  anaerobes;  that  is, 
organisms  which  will  grow  either  with  or  without  free  oxygen. 
These  bacteria  were  isolated  and  grown  on  the  egg-pork  medium, 
but  failed  to  give  any  characteristic  sour  or  putrefactive  odors,  and 
were  therefore  discarded. 

A  series  of  sound  hams,  all  of  them  of  mild  cure — that  is,  hams 
which  had  been  pumped  in  the  shank  only — were  also  examined 
bacteriologically.  In  examining  these  hams  cultures  were  taken 
at  varying  depths,  beginning  at  the  skinned  surface  and  going  back- 
ward toward  the  fat.  Cultures  were  also  taken  from  the  bone 
marrow  of   the  femur.     In   the   cultures   taken  near  the   skinned 


INOCULATION   EXPERIMENTS   WITH    HAMS.  21 

surfaces  the  ordinary  pickle  bacteria  were  obtained,  but  these  did 
not,  as  a  rule,  extend  beyond  a  depth  of  3  centimeters  below  the 
skinned  surface.  The  cultures  taken  from  the  deeper  portions  of 
the  hams  and  from  the  bone  marrow  of  the  femur  were  entirely 
negative — that  is,  failed  to  show  any  growth — and  the  anaerobic 
bacillus  noted  in  the  sour  hams  was  not  encountered  in  any  of  the 
cultures  made  from   these  hams. 

The  anaerobic  bacillus  isolated  from  the  sour  hams  was  found 
to  correspond  in  morphology  with  the  organism  noted  in  the  micro- 
scopic sections  made  from  the  muscular  tissue.  In  view  of  this 
fact  and  the  fact  that  it  was  constantly  present  in  the  sour  hams 
examined,  and  was  capable  of  producing  in  egg-pork  cultures  a 
sour-meat  odor  of  the  same  nature  as  that  obtained  from  sour  hams, 
this  organism  was  subjected  to  further  study  and  experimentation. 

INOCULATION    EXPERIMENTS    WITH    HAMS. 

The  experiments  which  follow  were  conducted  at  two  different 
packing  establishments  in  one  of  the  larger  packing  centers  of  the 
country.  The  officials  at  each  of  these  establishments  showed 
great  interest  in  the  experiments  and  were  most  courteous  and 
obliging  in  supplying  the  necessary  materials. 

The  first  question  to  be  decided  was  whether  the  bacillus  isolated 
from  sour  hams  was  actually  capable  of  causing  ham  souring.  The 
bacillus  in  question  had,  when  cultivated  on  the  egg-pork  medium, 
given  rise  to  a  sour  odor  similar  to  that  obtained  from  sour  hams, 
but  this  was  not  regarded  as  proof  positive  that  the  organism  was  the 
actual  cause  of  souring  in  hams.  The  proper  way  to  decide  this 
point  seemed  to  be  to  inoculate  hams  with  the  bacillus  and  then 
subject  these  hams  to  the  regular  method  of  cure  and  see  whether 
they  became  sour,  just  as  the  pathogenic  properties  of  a  disease- 
producing  organism  are  determined  by  the  inoculation  of  experiment 
animals.  The  first  two  experiments  which  follow  were  designed 
to  decide  this  point. 

It  was  regarded  as  important  to  conduct  similar  experiments 
at  two  different  establishments,  in  order  to  determine  whether  the 
same  results  would  be  obtained  under  the  somewhat  different  condi- 
tions imposed  by  different  methods  of  cure.  The  two  experiments 
which  follow  were  carried  out,  therefore,  at  different  establishments. 

Experiment  I. 

In  carrying  out  this  experiment  four  tierces  of  hams  were  ''put 
down"  or  "packed" — that  is,  placed  in  cure.  Two  of  the  tierces 
were  given  the  f  ancj'  or  mild  cure  and  two  the  regular  or  stronger  cure. 
The  hams  in  two  of  the  tierces,  one  mild  and  one  regular  cure,  were 
injected  with  a  culture  suspension  of  the  bacillus;  the  other  two  tierces 
were  not  injected  with  culture  and  were  put  down  to  serve  as  checks  on 


22  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

the  cure.  Hams  weighing  from  12  to  14  pounds  were  used  for  the  mild 
cure,  while  for  the  regular  cure  hams  weighing  from  14  to  16  pounds 
were  used.  This  was  in  accordance  with  the  general  rule  which  pre- 
vails in  packing  houses,  the  lighter  hams  being  subjected  to  the  mild 
cure  and  the  heavier  hams  to  the  regular  cure.  The  only  difference 
between  the  mild  and  the  regular  cure  in  this  experiment  lay  in  the 
pumping.  The  hams  which  were  given  the  mild  cure  were  pumped 
in  the  shank  only,  while  those  given  the  regular  cure  were  pumped 
in  the  body  as  well  as  in  the  shank. 

All  of  the  hams  had  received  the  usual  48-hour  chill.  They  were 
all  pumped  with  the  same  pumping  pickle  and  cured  in  the  same 
curing  pickle,  and  were  in  cure  for  the  same  length  of  time.  The 
pumping  and  curing  pickles  used  were  the  regular  pumping  and 
curing  pickles  of  the  establishment  at  which  the  experiment  was 
carried  out,  and  the  hams  were  cured  in  accordance  with  the  fancy 
and  regular  cures  as  practiced  at  this  establishment. 

The  hams  were  packed  in  new  tierces  which  had  been  thoroughly 
scalded  with  boiling  water.  The  tierces  were  held  in  a  curing  room 
which  was  kept  at  an  average  temperature  of  from  34°  to  36°  F., 
the  temperature  occasionally  going  as  high  as  38°  and  40°  F.,  but 
never  above  40°  F.  The  hams  were  left  in  cure  for  about  70 
days,  which  is  a  little  longer  than  the  usual  cure.  The  tierces  were 
rolled  three  times  during  the  cure.  At  the  end  of  the  cure  the  hams 
in  all  four  tierces  were  carefully  tested  by  an  expert  meat  inspector, 
who  knew  nothing  of  the  treatment  which  the  hams  had  received. 

The  hams  in  two  of  the  tierces  were  inoculated  with  a  culture 
suspension  prepared  as  follows:  Ten  tubes  of  egg-pork  medium,  each 
tube  containing  approximately  10  cubic  centimeters  of  the  medium, 
were  inoculated  with  the  bacillus  and  held  at  room  temperature 
(20°  to  25°  C.)  for  six  days.  The  cultures  were  then  filtered  through 
sterile  gauze  into  a  large  sterile  flask;  this  was  done  in  order  to 
remove  the  particles  of  meat,  which  might  otherwise  have  clogged 
the  syringes  used  in  inoculating  the  hams.  In  transferring  the  con- 
tents of  the  culture  tubes  to  the  filter  the  tubes  were  washed  out 
with  sterile  physiological  salt  solution  (0.6  per  cent  sodium  chlorid), 
and  the  meat  particles  on  the  filter  were  afterwards  washed  with 
the  salt  solution,  a  sufficient  quantity  of  the  latter  being  used  to 
bring  the  total  volume  of  filtrate  to  400  cubic  centimeters.  A 
microscopic  preparation  from  the  filtrate  showed  the  organisms  in 
large  numbers,  with  an  occasional  rod  showing  a  large  terminal 
spore.  This  suspension  was  used  for  the  injection  of  40  hams,  each 
ham  being  given  10  cubic  centimeters,  ok  the  equivalent  of  2.5  cubic 
centimeters  of  the  original  culture.  The  hams  were  injected  with  the 
culture  suspension  by  means  of  a  sterile  syringe  carrying  a  long  5-inch 
needle.  The  needle  was  thrust  well  into  the  body  of  the  ham  at  a 
point  near  the  upper  end  of  the  middle  bone  or  femur,  the  latter 


INOCULATION  EXPEEIMENTS   WITH   HAMS.  23 

being  used  as  a  guide  in  inserting  the  needle  and  the  injection  being 
made  into  the  tissues  just  behind  and  a  Uttle  to  one  side  of  the 
upper  end  of  the  femur. 

The  details  of  the  experiment  were  as  follows: 

Tierce  No.  1  (Janaj  cure). — This  tierce  contained  20  hama  weighing  from  12  to  14 
pounds  each.  These  hams  were  pumped  in  the  shank  only.  Immediately  after 
pumping  they  were  injected  with  10  cubic  centimeters  each  of  the  liquid  culture 
or  suspension  described  above.  After  injection  the  hams  were  immediately  packed 
in  the  tierce,  which  was  then  headed  up,  filled  with  the  regular  curing  pickle,  and 
placed  in  cure. 

Result:  When  tested  at  the  end  of  the  cure  all  of  the  hams  in  this  tierce  save  one 
were  found  to  be  sour.  In  10  of  them  the  souring  was  very  marked  throughout  the 
body  of  the  ham  and  extended  into  the  shank  as  well.  In  six  the  souring  was  very 
marked  in  the  body  of  the  ham,  but  did  not  extend  into  the  shank.  In  three  there 
was  slight  but  well-marked  souring  in  the  body  of  the  ham  with  no  souring  in  the 
shank,  and  one  remained  sweet.  The  probable  explanation  of  the  variation  in 
the  degree  and  the  extent  of  the  souring  will  be  discussed  later.  The  bone  marrow 
of  the  femur  or  middle  bone  was  tested  in  all  of  the  hams  and  found  to  be  sour  in 
18.  In  one  of  the  hams  which  showed  only  slight  souring  in  the  body  the  souring 
did  not  extend  through  to  the  bone  marrow,  and  in  the  ham  which  remained  sweet 
the  bone  marrow  was  also  sweet.  The  fact  that  one  ham  in  this  tierce  remained 
sweet  was  in  all  likelihood  due  to  an  oversight  in  making  the  inoculations.  In  making 
the  inoculations  the  hams  were  spread  out  in  a  row  on  a  table  by  a  packing-house 
assistant,  who  removed  the  hams  as  soon  as  they  were  inoculated  and  placed  them  in 
tierces;  and  it  is  more  than  probable  that  the  assistant  removed  one  of  the  hams  before 
it  was  inoculated  in  the  interval  when  the  writer  was  busy  filling  the  syringe  for 
the  next  inoculation. 

Tierce  No.  2  {fancy  cure). — This  tierce  contained  20  hams  of  the  same  average  weight 
as  the  preceding.  They  were  pumped  in  the  shank  only,  but  were  not  injected  with 
culture,  being  put  down  to  serve  as  checks  on  the  hams  in  tierce  No.  1.  These  hams, 
therefore,  were  subjected  to  exactly  the  same  cure  and  were  held  under  exactly  the 
same  conditions  as  those  in  tierce  No.  1,  the  only  difference  being  that  the  hams  in 
this  tierce  were  not  injected  with  culture. 

Result:  When  tested  at  the  end  of  the  cure  all  of  the  hams  in  this  tierce  were  found 
to  be  perfectly  sound  and  sweet,  showing  that  the  curing  in  this  instance  was  properly 
carried  out  and  that  the  souring  of  the  hams  in  tierce  No.  1  was  undoubtedly  due  to 
the  injections  of  culture  which  they  received. 

Tierce  No.  3  (regular  cure).—T!\v\a  tierce  contained  20  hams  weighing  from  14  to 
16  pounds  each.  These  hams  were  pumped  in  the  shank  and  also  in  the  body.  Imme- 
diately after  pumping  they  were  each  injected  in  the  same  manner  as  those  in  tierce 
No.  1  with  10  cubic  centimeters  of  culture.  The  hams  were  then  packed  in  tierce  and 
placed  in  cure. 

Result:  At  the  end  of  the  cure  9  of  the  hams  were  found  to  be  sour,  while  11 
remained  sweet.  Of  the  9  hams  which  became  sour,  1  showed  very  pronounced  sour- 
ing in  the  body  and  in  the  shank  as  well,  3  showed  very  pronounced  souring  in  the 
body,  1  showed  pronounced  souring  in  the  body,  and  4  slight  souring  in  the  body. 
The  bone  marrow  of  the  femur  was  tested  in  all  of  the  sour  hams  and  was  found  to  be 
sour  in  7.  In  2  of  the  sour  hams  which  showed  slight  souring  in  the  body  the  soueing 
noted  in  the  meat  had  not  extended  through  to  the  bone  marrow. 

Tierce  No.  4  {regular  cure). — This  tierce  contained  20  hams  of  the  same  average  weight 
as  those  in  tierce  No.  3,  and,  like  the  latter,  were  pumped  in  both  shank  and  body,  but 
were  not  injected  with  culture.  This  tierce  was  put  down  to  serve  as  a  check  on 
tierce  No.  3  and  was  held  under  exactly  the  same  conditions,  the  only  difference  being 
that  these  hams  were  not  injected  with  culture. 


24 


A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 


Result:  At  the  end  of  the  cure  the  hams  were  carefully  tested  and  all  were  found  to 
be  perfectly  sound  and  sweet. 

Results  of  Experiment  I. 


Number 
of  hams. 

Average 
weight 
of  hams. 

Cure. 

How  pumped. 

Treatment. 

Condition  at  end 
of  cure. 

No.  of 
tierce. 

Number 
of  sour 
hams. 

Per- 
centage 
of  sour 
hams. 

1 
2 

20 
20 
20 
20 

Pounds. 
12-14 

12-14 

14-16 

14-16 

Fancy . . 
...do 

Regular. 
...do 

Shank  only 

do 

Each  ham  injected 
with  10  c.  c.  of  cul- 
ture. 

Not  injected  with  cul- 
ture; check  on 
tiercel. 

Each  ham  Injected 
with  10  c.  c.  of  cul- 
ture. 

Not  injected  with 
culture;  check  on 
tierce  3. 

19 
0 
9 
0 

95 
0 

3 

4 

Shank  and  body . . 
do 

45 
0 

Three  hams  from  each  tierce  were  selected  for  bacteriological  and 
histological  examination.  From  tierces  1  and  3,  which  contained 
the  injected  hams,  three  of  the  most  pronounced  "sours"  were 
selected  from  each  tierce.  In  examining  the  hams  bacteriologically 
the  following  method  was  adopted:  The  hams  were  sectioned  near 
the  center  of  the  body  and  the  larger  or  butt  end  turned  up  so  as  to 
expose  the  cut  surface.  A  cross  section  of  a  ham  thus  cut  is  shown 
in  figure  3. 

Cultures  were  taken  at  the  points  indicated  by  the  numbers  and 
from  the  exposed  bone  marrow  of  the  femur  by  first  searing  the  sur- 
face, and  then  taking  out  plugs  of  the  meat  or  marrow  by  means  of 
sterile  instruments.  The  plugs  of  meat  or  marrow  were  dropped 
into  tubes  containing  egg-pork  medium  and  pushed  to  the  bottom  of 
the  tubes  by  means  of  a  sterile  platinum  wire.  In  the  cultures  made 
from  the  sour  hams  from  tierces  1  and  3,  which  were  injected  with 
culture,  the  bacillus  with  which  these  hams  were  injected- was  found 
in  practically  every  culture,  although  it  was  sometimes  absent  in. 
the  cultures  taken  at  points  near  the  skinned  surfaces  of  the  hams 
(i.  e.,  at  points  1,  4,  and  5  in  fig.  3).  In  the  cultures  taken  from  the 
meat,  the  bacillus  was  not  always  present  in  pure  culture,  but  this  is 
not  to  be  wondered  at  when  we  remember  that  the  pickling  fluids 
often  contain  large  numbers  of  bacteria  of  various  kinds,  and  these, 
of  course,  find  their  way  into  the  hams  in  the  pickling  fluids.  Espe- 
cially is  this  true  of  the  hams  which  are  pumped  in  the  body,  where 
bacteria  are  actually  pumped  into  the  bodies  of  the  hams  in  the 
pumping  pickle.  In  the  case  of  hams  which  are  not  pumped  in 
the  body,  the  pickle  bacteria  do  not  appear  to  penetrate  the  body  of 
the  ham  to  any  great  depth. 


INOCULATION    EXPERIMENTS    WITH    HAMS. 


25 


In  figure  3  the  plus  signs  after  the  figures  represent  the  distribution 
of  the  sour-ham  bacillus  in  one  of  the  hams  from  tierce  1,  and  this 
may  be  taken  as  a  typical  example  of  the  other  sour  hams  which  were 
examined  in  this  experiment.  It  should  be  explained  that  the 
shaded  areas  are  not  intended  to  represent  the  actual  limits  of  sour- 
ing, but  simply  the  areas  in  which  the  sour  odor  was  most  pronounced 
and  from  which  it  could  be  readily  obtained  with  the  trier.  In 
comparing  the  regular  and  mild  cure  hams,  it  was  found  that  the 
areas  of  souring  as  defined  with  the  trier  were  more  restricted  in  the 
regular  cure  hams,  and  this  was  undoubtedly  due  to  the  additional 
pumping  which  these  hams  received,  whereby  the  growth  of  the 
bacillus  was  partially  inhibited. 


SHin 


Fig.  3.— Cross  section  through  body  of  artificially  soured  ham,  showing  sour  areas  and  points  at  which 
cultures  were  taken.  Darker  shading  indicates  sour  area  in  hams  pumped  in  body  and  shank;  light 
shading  indicates  sour  area  in  hams  pumped  in  shank  only;  figures  indicate  points  at  which  cultures 
were  taken;  plus  signs  indicate  presence  of  bacillus;  minus  sign  indicates  absence  of  bacillus;  X  indi- 
cates point  of  inoculation. 

It  will  be  noticed  that  the  sour-ham  bacillus  was  present  in  cul- 
tures taken  at  points  outside  the  shaded  areas,  indicating  that  the 
organism  had  extended  generally  throughout  the  bodies  of  the  hams. 
As  the  hams  were  inoculated  at  a  point  just  to  one  side  of  and  a 
little  behind  the  femur  (i.  e.,  at  the  point  X  in  the  figure),  the  pres- 
ence of  the  bacillus  generally  throughout  the  hams  would  indicate 
a  very  extensive  multiplication  of  the  original  bacilli  with  which  the 
hams  were  injected.  In  view  of  the  fact  that  the  bacillus  in  question 
is  nonmotile,  the  spread  of  the  bacilli  throughout  the  hams  must 
result  simply  from  subdivision  and  growth  by  extension,  and  in 
spreading  throughout  the  hams  the  bacilli  appear  to  follow  along  the 
connective  tissue  bands  which  afi'ord  paths  of  least  resistance.  In  the 
cultures  made  from  the  bone  marrow  the  bacillus  was  recovered  in 
70973°— Bull.  132—11 4 


26  A   BACTERIOLOGICAL  STUDY   OF    HAM    SOURING. 

pure  culture  from  each  of  the  hams  examined,  and  it  is  probable  that 
the  bacillus  finds  its  way  into  the  bone  marrow  from  the  meat  by 
following  along  the  small  arteries  which  pass  through  the  bone.  The 
fact  that  the  bacillus  was  found  in  pure  culture  (i.  e.,  uncontaminated) 
in  the  cultures  made  from  the  bone  marrow  is  explained  probably 
by  its  capacity  for  growth  by  extension,  and  also  by  the  fact  that  the 
pickling  solutions  probably  do  not  reach  the  bone  marrow  until  late 
in  the  curing  and  then  only  to  a  limited  extent.  The  bacteria  which 
ordinarily  occur  in  pickling  fluids  are  not  strict  anaerobes  and  are  not 
placed  under  the  most  suitable  conditions  for  growth  when  they 
reach  the  interior  of  the  ham,  for  it  seems  probable  that  in  the  inte- 
rior of  hams  which  are  totally  submerged  in  pickling  fluids  the  amount 
of  available  oxygen  must  be  extremely  small.  The  ordinary  pickle 
bacteria,  therefore,  would  not  multiply  as  rapidly  in  the  interior  of 
the  hams  and  would  not  find  their  way  into  the  bone  marrow  as 
soon  as  would  a  strictly  anaerobic  organism. 

Pure  cultures  of  the  sour-ham  bacillus,  recovered  from  the  meat 
and  bone  marrow  of  the  injected  hams,  were  compared  with  cul- 
tures of  the  original  bacillus  used  for  inoculating  the  hams,  and 
were  found  to  be  identical.  Furthermore,  the  bacillus  with  which 
the  hams  were  injected  was  recovered  from  the  injected  hams  at 
points  far  removed  from  the  original  point  of  injection,  showing  that 
the  organism  had  multiplied  and  extended  throughout  the  bodies  of 
the  hams  and  that  it  was  clearly  responsible  for  the  souring  which 
the  hams  had  undergone. 

Sound  hams  from  tierces  2  and  4  were  examined  bacteriologically 
in  the  same  manner  as  the  injected  hams,  and  some  of  the  cultures 
showed  the  ordinary  pickle  bacteria,  but  in  not  a  single  instance  did 
egg-pork  cultures  yield  a  sour  odor,  and  in  no  case  could  the  sour- 
ham  bacillus  be  demonstrated  in  any  of  these  hams. 

Microscopic  sections  and  teased  preparations  of  the  muscle  fibers 
in  salt  solution  were  prepared  from  several  of  the  sour  hams  in  this 
experiment,  and  these  preparations  showed  the  same  histological 
changes  and  the  same  distribution  of  bacilli  as  noted  in  the  natural 
sours. 

In  Plate  III,  figures  1  and  2,  sections  are  shown  of  artificially  soured 
hams,  that  is,  hams  which  were  artificially  soured  by  injections  of  cul- 
ture; and  if  these  figures  be  compared  with  the  sections  made  from 
hams  which  had  undergone  spontaneous  souring  (see  PI,  II,  figs.  1  and 
2)  the  similarity  in  the  form  and  distribution  of  the  bacilli  will  be  at 
once  apparent. 

Summary  and  discussion  of  Experiment  I. — Comparing  tierces  1 
and  2,  where  the  hams  were  pumped  in  the  shank  only,  the  only 
difference  being  that  the  hams  in  tierce  1  were  inoculated  with  culture 
wliile  those  in  tierce  2  were  not,  we  find  that  in  tierce  1  nineteen  out 


Buu  132,  Bureau  of  Animal  Industry,  U.  S.  Dept.  of  Agriculture. 


Plate  III. 


\A/"  I  U  f}  ~-^  Y-ri 


Fig.  1  .—Section  Through  Muscular  Tissue  of  Artificially  Soured 
Ham,  Showing  Distribution  of  Bacilli  Between  the  Muscle 
Fibers,  which  are  Shown  in  Cross  Section.  The  Dark  Lines  and 
Masses  Between  the  Muscle  Fibers  Represent  Clumps  of 
Bacilli. 

(Pen-and-ink   drawing   made  with  camera    lucidafrom  section  stained  by 
the  Gram-Weigert  method  to  show  bacteria,     x  86.) 


Fig.  2.— Section  Through  Muscular  Tissue  of  Artificially  Soured 
Ham,  Showing  Individual  Bacilli  Between  the  Muscle  Fibers, 
which  are  Cut  Longitudinally. 

(Pen-and-ink   drawing  made  with    camera  hicida  from  section   stained  by 
the  Gram-Weigert  method  to  show  bacteria,     x  320.) 


INOCULATION    EXPERIMENTS   WITH    HAMS.  27 

of  twenty,  or  95  per  cent,  of  the  hams  became  sour,  whereas  in  tierce  2 
all  of  the  hams  remained  sweet.  In  view  of  the  fact  that  these  tierces 
were  held  under  exactly  the  same  conditions,  we  must  conclude  that 
the  souring  of  the  hams  in  tierce  1  was  due  to  the  injection  of  culture 
which  they  received. 

Comparing  tierces  3  and  4,  where  the  hams  were  pumped  in  both 
shank  and  body,  the  hams  in  tierce  3  being  injected  with  culture 
while  those  in  tierce  4  were  not,  we  find  that  in  tierce  3  nine  out  of 
twenty,  or  45  per  cent,  of  the  hams  became  sour,  whereas  in  tierce  4  all 
of  the  hams  remained  sweet.  As  the  conditions  of  cure  were  the  same 
for  all  four  tierces,  we  must  again  conclude  that  the  souring  of  the 
hams  in  tierce  3  was  directly  attributable  to  the  injections  of  culture 
which  they  received. 

If  now  we  compare  tierces  1  and  3,  the  two  tierces  which  were 
injected  with  culture,  we  find  that  in  the  case  of  tierce  1,  where  the 
hams  were  pumped  in  the  shank  only,  95  per  cent  became  sour,' 
whereas  in  the  case  of  tierce  3,  where  the  hams  were  pumped  in  both 
shank  and  body,  only  45  per  cent  became  sour.  In  other  words,  the 
percentage  of  souring  in  those  hams  which  were  pumped  in  the  body 
as  well  as  in  the  shank  was  50  per  cent  less  than  in  those  hams  which 
were  pumped  in  the  shank  only.  Inasmuch  as  the  only  difference 
in  the  treatment  accorded  tierces  1  and  3  lay  in  the  additional 
pumping  given  the  hams  in  tierce  3,  we  must  conclude  that  the 
marked  diminution  in  the  percentage  of  souring  in  the  case  of  tierce 
3  was  undoubtedly  due  to  the  additional  pumping  which  these  hams 
received,  the  hams  being  saturated  at  the  start  with  the  pumping 
pickle.  It  will  be  shown  later  that  both  sodium  chlorid  and  potas- 
sium nitrate  exert  an  inhibitory  effect  upon  the  bacillus  with  which  the 
hams  were  injected,  which  directly  bears  out  the  foregoing  conclusion. 

In  tierces  2  and  4,  the  two  check  tierces  which  were  not  injected 
with  culture,  all  of  the  hams  were  sweet  at  the  end  of  the  cure,  showing 
that  the  conditions  under  which  the  experiment  was  carried  out  were 
entirely  favorable  to  a  successful  cure. 

The  sour  odor  obtained  from  the  artificially  soured  hams  in  this 
experiment  was  pronounced  by  the  meat  inspector  who  tested  the 
hams,  and  who  was  entirely  unaware  of  the  treatment  they  had 
received,  to  be  identical  with  the  usual  sour  odor  which  characterizes 
hams  that  have  undergone  spontaneous  souring;  in  other  words, 
there  was  no  difference  in  odor  between  these  artificially  soured  hams 
and  natural  sours. 

With  regard  to  the  variation  in  the  degree  and  the  extent  of  the 
souring  exhibited  by  the  individual  hams  in  the  two  inoculated 
tierces,  where  some  of  the  hams  showed  pronounced  souring  through- 
out the  body  and  shank,  while  others  which  had  been  injected  with 
the  same  amount  of  culture  showed  only  slight  souring  in  the  body, 


28  A   BACTERIOLOGICAL  STUDY   OF    HAM   SOURING. 

several  factors  must  be  considered,  viz:  (1)  Differences  in  the  reaction 
of  the  meat  of  the  individual  hams  which  may  have  exerted  an  influ- 
ence on  the  growth  of  the  bacteria  with  which  the  hams  were  injected. 

(2)  Variations  in  the  texture  of  the  muscle  fibers  and  connective 
tissue  of  the  individual  hams,  permitting  in  some  cases  a  more  rapid 
and  thorough  penetration  of  the  pickling  fluids  to  the  interior  of  the 
hams,  whereby  the  inhibitory  effect  of  the  sodium  chlorid  and  the 
potassium  nitrate  on  the  bacteria  would  come  into  play  earlier. 

(3)  Variations  in  pumping,  whereby  more  of  the  pickling  solution  was 
forced  into  some  of  the  hams  than  into  others.  Probably  all  three  of 
these  factors  would  have  to  be  taken  into  account  in  explaining  the 
variation  in  the  degree  and  extent  of  the  souring  exhibited  by  the 
injected  hams. 

With  regard  to  the  souring  of  the  bone  marrow,  we  find  that  of 
nineteen  sour  hams  in  tierce  1  eighteen  showed  sour  marrows,  while 
in  tierce  3  nine  sour  hams  showed  seven  sour  marrows.  The  high 
pnoportion  of  marrow  sours  is  not  surprising  when  it  is  recalled  that 
of  the  nineteen  sour  hams  in  tierce  1  the  meat  was  markedly  sour  in 
sixteen,  while  of  the  nine  sour  hams  in  tierce  3  the  meat  was  mark- 
edly sour  in  five.  In  the  case  of  the  four  sour  hams  in  tierce  3 
which  showed  slight  souring  in  the  body,  two  of  these  showed  sour 
marrows,  while  in  two  the  marrows  were  sweet.  In  this  experiment 
the  percentage  of  sour  hams  showing  sour  marrows  corresponds 
with  the  percentage  of  marrow-sour  hams  found  in  the  packing 
house,  where,  as  has  been  pointed  out  before,  a  ham  which  is  mark- 
edly sour  in  the  body  will  practically  always  show  sour  marrow, 
while  in  hams  which  show  only  slight  souring  in  the  body  the  mar- 
row is  involved  in  about  50  per  cent  of  Ihe  cases. 

Experiment  II. 

This  experiment  was  essentially  a  repetition  of  Experiment  I,  but 
was  carried  out  at  a  different  packing  establishment  and  under  some- 
what different  conditions. 

Two  lots  of  hams  were  injected  with  a  culture  suspension  of  the 
bacillus  at  different  stages  of  the  cure,  or  rather  at  different  stages  in 
the  preparation  for  cure,  i.  e.,  (1)  on  the  hanging  floor,  previous  to 
chillmg,  and  (2)  after  chilling  and  pumping  and  immediately  before 
packing.  Three  tierces,  each  containing  20  hams,  were  put  down. 
Two  of  the  tierces  contained  the  hams  injected  with  culture,  wliile 
the  thu-d  tierce  contained  check  hams  which  had  not  been  treated 
with  culture.  Half  of  the  hams  in  each  tierce  were  pumped 
m  the  shank,  while  the  other  half  were  pumped  in  both  body  and 
shank.  The  same  pumping  and  curing  pickles  were  used  for  all  three 
tierces,  and  were  the  regular  pumping  and  regular  curing  pickles  of 
the  establishment  at  which  tJie  experiment  was  carried  out.     The 


INOCULATION    EXPERIMENTS   WITH    HAMS,  29 

hams  used  were  all  14  to  16  pounds  in  weight  and  were  subjected  to 
the  usual  48-hour  chill  with  an  additional  chill  of  48  hours  after  they 
were  cut  from  the  carcass.  They  were  packed  in  tierces  which  had 
been  thorougldy  scrubbed  and  cleaned  with  boiling  water.  The 
tierces  were  held  in  a  pickling  room  at  a  temperature  of  33°  to  36°  F., 
the  temperature  never  rising  above  36°  F.,  and  were  rolled  three 
times  during  the  curing  period.  The  hams  were  in  cure  for  about 
eighty  days.  At  the  end  of  the  cure  the  hams  were  carefully  tested  by 
a  trained  meat  inspector,  who  knew  nothing  of  the  treatment  they 
had  received. 

The  culture  suspension  was  prepared  from  20  tubes  of  egg-pork 
medium  in  the  same  manner  as  that  used  in  Experiment  I,  the  cultures 
being  diluted  with  sufficient  salt  solution  to  give  400  cubic  centimeters 
of  suspension.  The  cultures  from  which  the  suspension  was  prepared 
had  grown  at  room  temperature  for  ten  days.  The  suspension  was 
examined  microscopically  and  showed  large  numbers  of  the  bacilli  in 
the  form  of  filaments  or  long  chains,  with  many- of  the  individual 
organisms  showing  large  terminal  spores.  The  hams  were  injected 
with  the  culture  suspension  in  the  same  manner  as  those  in  Experi- 
ment I. 

The  details  of  the  experiment  were  as  follows: 

Tierce  No.  1. — Contained  20  hams,  each  ham  being  injected  with  20  cubic  centi- 
meters of  the  suspension  or  the  equivalent  of  10  cubic  centimeters  of  the  original 
culture.'  The  hams  were  injected  while  on  the  hanging  floor,  before  they  had  been 
cut  from  the  carcasses  and  previous  to  chilling.  The  carcasses  were  still  quite  warm — 
that  is,  had  lost  but  little  of  their  body  heat  when  the  injections  were  made.  The 
<arcasses,  which  had  been  carefully  tagged,  were  then  run  into  coolers  and  given 
the  usual  48-hour  chill,  after  which  the  hams  were  severed  from  the  carcasses  and 
given  an  additional  48-hour  chill  in  accordance  with  the  custom  of  the  packing 
house  at  which  the  experiment  was  carried  out.  The  hams  were  next  pumped  with 
regular  pumping  pickle,  10  being  pumped  in  both  body  and  shank  and  10  in  shank 
only.  They  were  finally  packed  in  a  tierce,  which  was  then  headed  up,  filled  with 
regular  curing  pickle,  and  placed  in  cure. 

Result:  WTien  tested  at  the  end  of  the  cure  it  was  found  that  the  10  hams  which 
were  pumped  in  the  shank  only  were  all  sour.  In  each  of  them  the  souring  extended 
throughout  the  entire  ham,  in  the  shank  as  well  as  in  the  body,  and  was  very  pro- 
nounced, so  much  so  that  they  were  characterized  as  "stinkers  "  by  the  meat  inspector 
who  assisted  in  testing  them.  The  bone  marrow  of  the  femur  or  middle  bone  was 
sour  in  all  of  these  hams.  Of  the  10  hams  which  were  pumped  in  both  body  and 
shank  7  showed  well-marked  souring  throughout  the  body,  but  the  souring  did  not 
extend  into  the  shank.  The  bone  marrow  of  the  femur  was  found  to  be  sour  in  6  of 
these  hams,  while  in  1  the  souring  had  not  extended  through  to  the  bone  marrow. 

Tierce  No.  2. — Contained  20  hams  which  were  chilled  and  pumped  in  exactly  the 
same  manner  as  those  in  tierce  No.  1.  These  hams  were  injected  with  culture  after 
they  had  been  chilled  and  pumped,  or  just  before  they  were  placed  in  cure.  The 
hams  in  this  tierce,  therefore,  were  injected  with  culture  four  days  later  than  those 
in  tierce  1.  The  hams  were  injected  with  a  bacterial  suspension  prepared  in  the 
same  manner  as  that  used  for  tierce  1,  except  that  the  egg-pork  cultures  from  which 
the  suspension  was  prepared  were  7  days  instead  of  10  days  old.     Each  ham  was 


30 


A   BACTERIOLOGICAL   STUDY   OF    HAM    SOURING. 


injected  with  20  cubic  centimeters  of  the  suspension  or  the  equivalent  of  10  cubic 
IhT^nZi  1  ""'^'"''^  '"^'"'■''  ^^'  ^'™'  ""'"''  '"^"'*'^  ^^  *^"  ^"^^  ^^^°«''  ^« 
Result:  When  tested  at  the  end  of  the  cure,  it  was  found  that  of  the  10  hams  which 
were  pumped  in  the  shank  all  were  sour;  in  8  of  these  the  souring  was  very  marked 
throughout  the  body  of  the  ham  and  extended  into  the  shank;  in  all  of  these  hams 
m  .rTi^  f  5f  ^•^^  ^^••^"g^  t°  the  bone  marrow  of  the  middle  bone  or  femur 
Of  the  10  hams  which  were  pumped  in  both  body  and  shank  6  were  sour  in  the  body" 
These  hams  were  classed  by  the  meat  inspector  who  examined  them  as  "light  bodv 
sours,  and  in  none  of  them  did  the  souring  extend  into  the  shank  or  through  the 
Done  into  the  bone  marrow  of  the  femur. 

Tierce  No  S .-Contained  20  hams  which  were  chUled  and  pumped  in  the  same 
manner  as  those  in  the  two  preceding  tierces.  These  hams  were  not  injected  with 
culture  and  were  put  down  to  serve  as  checks  on  the  cure.  In  other  words  thev 
were  pumped  with  the  same  pickling  fluids,  were  subjected  to  exactly  the  same  cure 
and  were  held  under  precisely  the  same  conditions  as  those  in  the  preceding  tierces' 
the  only  difference  being  that  the  hams  in  this  tierce  were  not  injected  with  culture' 
Kesult.-  WTien  tested  at  the  end  of  the  cure,  all  of  the  hams  in  this  tierce  were  found 
to  be  perfectly  sound  and  sweet. 


Results  of  Experiment  II. 


No.  of 
tierce. 


Number 
of  hams. 


Average 

weight  of 

hams. 


Pmivds. 
14-16 

14-16 
14-16 


How  pumped. 


10  in  shank. 


.10  in  body  and  shank. 
10  in  shank 


Treatment. 


Gondii  ion  at  end  of 
cure. 


Each  ham  injected  with  20 
c.  c.  of  culture  prior  to 
chilling  and  pumping. 

—  do 

Each  ham  injected  with.  20 

c.  c.  of  culture  subsequent 

,„ .    ,    J        J   ,  I      to  chilling  and  pumping. 

10  m  body  and  shank.. do..  ^      p    » 

J^ !"  shank . .   Not  injected  with  culture.' ." 

10  m  body  and  shan k. do 


Number  i  Percent- 
ofsour  jageofsour 
bams.        hams. 


10 


100 


7 

70 

lU 

100 

6 

60 

0 

0 

0 

0 

Four  hams  were  selected  from  each  tierce  for  bacteriological  and 
histological  examination.  From  tierces  1  and  2,  in  which,  the  hams 
were  injected  with  culture,  4  of  the  sourest  hams  were  selected  from 
each  tierce.  Cultures  were  made  from  these  hams  in  the  same 
manner  as  described  under  Experiment  I  and  with  the  same  result- 
that  IS,  the  sour-ham  bacillus  was  found  throughout  the  bodies  of 
the  hams.  Microscopic  sections  were  also  prepared  from  these  hams 
and  showed  the  same  histological  changes  and  the  same  distribution 
of  bacilh  as  noted  for  the  hams  in  Experiment  I. 

Summary  and  discussion  of  Expenment  //.—Comparing  tierces  1 
and  2,  in  which  the  hams  were  injected  with  culture,  with  tierce  3, 
where  the  hams  were  not  injected  with  culture,  we  find  that  in  tierce 
1  seventeen  hams  (85  per  cent)  became  sour  and  in  tierce  2  sixteen 
hams  (80  per  cent)  became  sour,  whereas  in  tierce  3  all  of  the  hams 


INOCULATION   EXPERIMENTS   WITH   HAMS.  31 

were  sweet.  The  fact  that  all  of  the  hams  in  tierce  3,  the  check 
tierce,  were  sweet  indicates  that  the  conditions  were  favorable  for  a 
successful  cure ;  and  as  all  three  tierces  were  cured  under  exactly  the 
same  conditions,  the  only  difference  being  that  the  hams  in  tierces 
1  and  2  were  injected  with  culture,  whereas  those  in  tierce  3  were  not 
injected  with  culture,  we  must  conclude  that  the  souring  of  the  hams 
in  tierces  1  and  2  was  due  to  the  injections  of  culture  which  they 
received. 

Comparing  tierce  1  with  tierce  2,  we  find  that  the  hams  in  tierce  1 
showed  more  extensive  souring  than  did  those  in  tierce  2,  this  being 
especially  noticeable  in  the  case  of  the  hams  which  were  pumped  in 
both  body  and  shank.  This  difference  in  the  extent  or  degree  of  sour- 
ing was  probably  due  to  the  fact  that  the  hams  in  tierce  1  were 
injected  while  they  were  still  warm  and  before  they  had  lost  their 
animal  heat,  the  bacterial  suspension  thus  having  a  better  chance  to 
become  disseminated  through  the  meat.  The  hams  in  tierce  2  were 
injected  with  culture  after  they  had  been  chilled,  when  the  tissues 
were  more  or  less  contracted  and  the  conditions  less  favorable  for  the 
dissemination  of  th'e  suspension  throughout  the  meat.  The  hams  in 
tierce  1  were  also  injected  four  days  earlier  than  those  in  tierce  2, 
and  prior  to  pumping;  and  this  would  explain  the  greater  difference 
in  the  extent  of  the  souring  in  the  case  of  the  hams  which  were 
pumped  in  both  body  and  shank,  as  in  tierce  1  the  bacteria  had  four 
days  in  which  to  develop  before  coming  in  contact  with  the  pickling 
fluids,  whereas  in  tierce  2  the  bacteria  were  injected  after  the  hams 
were  pumped  with  pickle  and  were  thus  brought  into  immediate 
contact  with  the  pickling  fluids,  which,  as  will  be  shown  later,  have  a 
distinct  inhibitory  action  upon  the  bacillus  in  question.  In  the  case 
of  the  hams  which  were  pumped  in  the  shank  but  not  in  the  body 
there  was  not  this  difference,  as  in  these  hams  the  pickling  fluids 
must  penetrate  into  the  bodies  of  the  hams  from  the  outside.  As  it 
requires  some  time  for  the  pickling  fluids  to  reach  the  interior  of  a 
ham,  the  bacteria  were  thus  afforded  quite  an  interval  in  which  to 
develop  before  being  exposed  to  the  inhibitory  action  of  the  pickling 
fluids.  A  chemical  study  of  the  processes  involved  in  ham  curing 
bas  been  carried  out  in  the  Biochemic  Division  and  the  approximate 
rate  of  penetration  of  the  curing  pickle  determined,  and  it  was  found 
that  it  required  about  four  weeks  for  the  interior  of  a  10-pound  ham 
which  had  not  been  pumped  to  acquire  its  maximum  percentage  of 
sodium  chlorid. 

To  recapitulate:  In  this  experiment  40  hams  were  injected  with 
culture,  half  of  this  number  being  pumped  in  the  shank  only  and 
half  in  both  body  and  shank.  Of  the  20  which  were  pumped  in  the 
shank  only,  every  ham  without  exception,  or  100  per  cent,  became 
sour.     Of  those  which  were  pumped  in  both  body  and  shank,  13,  or 


32  A   BACTERIOLOGICAL   STUDY   OF    HAM    SOURING. 

65  per  cent,  became  sour.  The  reduction  in  the  percentage  of  sours 
in  the  last  lot  was  clearly  due  to  the  additional  pumping  which  these 
hams  received. 

If  now  we  compare  tierce  2  in  this  experiment  with  tierces  1  and  3 
in  Experiment  I — these  three  tierces  being  comparable,  as  they  were 
all  injected  with  culture  at  the  same  stage  in  their  preparation  for 
cure,  that  is,  subsequent  to  chilling  and  pumping — we  find,  in  the 
case  of  the  hams  pumped  in  both  body  and  shank,  65  per  cent  of 
sours  in  Experiment  II  as  against  45  per  cent  in  Experiment  I,  and 
this  difference  is  undoubtedly  due  to  the  heavier  dose  of  culture 
used  in  Experiment  II,  where  the  hams  were  given  the  equivalent 
of  10  cubic  centimeters  of  egg-pork  culture  as  against  2^  cubic  cen- 
timeters in  Experiment  I.  In  the  case  of  the  hams  which  were 
pumped  in  the  shank  but  not  in  the  body,  the  percentage  of  sour^ 
was  practically  the  same  in  the  two  experiments — in  Experiment  I 
all  but  one  of  these  hams  became  sour,  while  in  Experiment  II  all  of 
them  became  sour.  The  degree  or  extent  of  the  souring  in  these  last 
hams,  however,  was  greater  in  Experiment  II,  a  result  of  the  heavier 
injections  of  culture  which  they  received. 

Summary  of  Experiments  I  and  II. 

Summarizing  the  results  obtained  in  Experiments  I  and  II,  we  find 
that  culture  suspensions  of  the  anaerobic  bacillus  isolated  from  sour 
hams  caused  souring  with  great  uniformity  when  injected  into  the 
bodies  of  sound  hams  which  were  pumped  in  the  shank  only.  In 
the  two  experiments,  40  sound  hams  which  were  pumped  in  the 
shank  only  were  injected  with  culture  suspensions  of  the  bacillus, 
with  the  result  that  39,  or  97.5  per  cent,  became  sour  during  the 
process  of  cure;  and  it  is  quite  probable,  as  we  have  pointed  out 
before,  that  one  of  these  hams  was  overlooked  in  making  the  inocu- 
lations, otherwise  the  entire  lot  would  have  become  sour. 

The  inhibitory  action  of  the  pickling  fluids  upon  the  bacillus  is 
well  shown  in  the  case  of  those  hams  which  were  pumped  in  both 
body  and  shank.  Out  of  40  hams  which  were  pumped  in  both  body 
and  shank,  22,  or  55  per  cent,  became  sour  in  the  process  of  curing. 
Inasmuch  as  these  hams  were  cured  under  precisely  the  same  condi- 
tions as  the  hams  which  were  pumped  in  the  shank  only,  we  must 
conclude  that  the  diminution  in  souring  in  these  hams  was  undoubt- 
edly due  to  the  additional  pumping  which  they  received,  whereby 
the  bacteria  with  which  these  hams  were  injected  were  brought  into 
immediate  contact  with  the  strong  pumping  pickle  and  their  devel- 
opment thereby  inhibited. 

In  these  two  experiments  it  was  proven  beyond  doubt  that  the 
anaerobic  bacillus  isolated  from  sour  hams  was  capable  of  producing 


PROBABLE   METHODS   OF   INFECTION.  33 

souring  when  introduced  into  the  bodies  of  sound  hams ;  and  in  view 
of  the  fact  that  this  bacillus  was  constantly  present  in  hams  which 
had  undergone  spontaneous  or  natural  souring,  and  was  the  only 
organism  that  could  be  isolated  from  such  hams  that  was  capable  of 
producing  in  egg-pork  cultures  the  characteristic  sour-ham  odor,  the 
conclusion  seems  justifiable  that  this  bacillus  is  an  undoubted  cause 
of  the  ham  souring  which  occurs  in  the  packing  house;  and  the 
results  thus  far  obtained  indicate  that  it  is  an  important,  if  not  the 
only,  factor  concerned  in  ham  souring. 

Having  established  the  etiological  relation  of  the  bacillus  isolated 
from  sour  hams  with  ham  souring,  the  next  point  to  be  considered 
was  the  manner  in  which  this  bacillus  finds  its  way  into  the  bodies  of 
the  hams. 

PROBABLE  METHOD  BY  WHICH  HAM-SOURING  BACILLUS  ENTERS  HAMS. 

Regarding  the  question  of  the  probable  method  by  which  the  ham- 
souring  bacillus  enters  hams,  there  were  three  possibilities  to  be  taken 
into  consideration:  (1)  That  the  bacillus  is  present  in  the  flesh  of 
hogs  at  the  time  of  slaughter,  (2)  that  the  bacillus  gains  entrance 
through  the  pickling  fluids,  (3)  that  the  bacillus  is  introduced  into 
the  bodies  of  the  hams  in  the  handling  or  manipulation  which  the 
hams  undergo  in  preparation  for,  or  during,  the  process  of  curing. 

Possibility  of  Infection-  Prior  to  Slaughter. 

In  order  to  throw  some  light  upon  this  point,  a  number  of  fresh 
hams — that  is,  hams  which  had  been  chilled  bvit  not  pumped  or  sub- 
jected to  any  other  manipulation — were  examined  bacteriologically, 
but  in  no  case  could  the  anaerobic  bacillus  which  was  isolated  from 
sour  hams  be  detected  in  any  of  them.  The  fact  that  in  certain 
of  the  smaller  packing  establishments  which  cure  their  hams  with- 
out pumping  the  percentage  of  souring  is  extremely  low  would  also 
seem  to  negative  this  possibility,  for  if  the  bacillus  which  causes 
souring  were  present  in  the  hams  at  the  time  of  slaughter,  sour  hams 
would  be  as  frequent  at  such  establishments  as  at  those  establish- 
ments which  make  a  practice  of  pumping.  Furthermore,  a  labora- 
tory study,  biological  and  chemical,  of  the  bacillus  isolated  from 
sour  hams  shows  that  this  organism  belongs  to  the  class  of  putre- 
factive bacteria,  and  while  such  bacteria  may  be  present  in  the 
intestines  of  health}^  animals,  as,  for  example,  the  bacillus  of  Bien- 
stock  (Bacillus  putrijicus),  these  bacteria  do  not  invade  the  organs 
and  tissues  of  the  body  until  after  the  death  of  the  animal,  and  the 
packing-house  practice  of  rapidly  eviscerating  the  hogs  immediately 
after  slaughter  would  certainly  preclude  this  possibility. 


34  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

Possible  Infection  prom  Pickling  Fluids. 

With  regard  to  the  second  possibility,  that  the  bacillus  finds  its 
way  into  the  hams  in  the  curing  pickles,  it  was  determined  by  labora- 
tory experiment  that  the  addition  of  3  per  cent  of  sodium  chlorid  or 
3  per  cent  of  potassium  nitrate  to  laboratory  media  completely 
inliibits  the  growth  of  the  bacillus.  As  the  pickling  solutions  always 
contain  considerably  more  than  these  percentages  of  sodium  chlorid 
and  potassium  nitrate,  it  would  be  impossible  for  the  bacillus  to 
multiply  in  the  pickles.  Additional  laboratory  experiments  demon- 
strated, however,  that  the  bacillus  or  its  spores  may  remain  alive  in 
the  curing  pickles  for  at  least  thirty  days,  and  it  seemed  possible  that 
the  curing  pickles  might  become  contaminated  at  times  with  the 
bacilli,  and  that  the  bacilli,  although  incapable  of  multiplying  in  the 
pickles,  might  find  their  way  into  the  bodies  of  the  hams  in  the 
pickling  fluids.  In  order  to  throw  some  light  upon  this  point,  the 
following  experiment  was  carried  out: 

EXPERIMENT  TO   SHOW    WHETHER  INFECTION  TAKES  PLACE  FROM  THE  CURING  PICKLE. 

In  this  experiment  two  tierces  were  put  down,  each  containing 
20  hams.  The  hams  weighed  from  14  to  16  pounds  and  had  received 
the  usual  48-hour  chilling.  The  pickhng  solutions  employed  were 
the  regular  curing  pickles  of  the  establishment  at  which  the  experi- 
ment was  carried  out.  The  curing  pickle  in  one  tierce  was  inoculated 
with  400  cubic  centimeters  of  a  culture  suspension  of  the  bacillus, 
prepared  in  the  same  manner  as  that  used  for  the  injection  of  the 
hams  in  tierce  2  in  Experiment  II.  A  microscopic  preparation  made 
from  a  small  drop  of  the  culture  suspension  before  adding  it  to  the 
pickle  showed  the  bacilli  in  large  numbers,  and  in  the  400  cubic 
centimeters  of  the  suspension  there  were  millions  of  the  bacteria. 
The  curing  pickle  in  the  other  tierce  was  left  untreated,  the  hams 
in  this  tierce  serving  as  a  check.  The  tierces  used  in  this  experiment, 
as  in  all  of  the  experiments,  were  thoroughly  cleaned  with  boiling 
water  before  the  hams  were  placed  in  them.  The  experiment  was 
conducted  in  a  pickling  room  which  was  held  at  33°  to  36°  F.,  and 
the  tierces  were  rolled  three  times  during  the  cure.  The  details  of 
the  experiment  are  as  follows: 

Tierce  1. — Contained  20  hams,  half  of  which  were  pumped  in  both  body  and  shank 
and  half  in  the  shank  only.  As  soon  as  they  were  pumped  the  hams  were  packed  in 
the  tierce.  Sufficient  curing  pickle  to  fill  the  tierce  was  then  measured  out  in  a  clean 
barrel  and  to  it  was  added  the  culture  suspension.  The  culture  was  thoroughly  mixed 
with  the  pickle  and  the  latter  was  then  run  into  the  tierce  containing  the  hams. 

Result:  When  tested  at  the  end  of  the  cure,  two  of  the  hams  which  had  been 
pumped  in  the  shank  only  showed  slight  souring  in  the  body.  The  rest  of  the  hams 
were  sweet. 

Ti^ce  2. — Contained  20  hams  which  were  pumped  in  the  same  manner  as  those  in 
tierce  1.     The  curing  pickle  was  the  same  as  that  used  for  tierce  1,  but  without  the 


INFECTION  THROUGH   MANIPULATION   OK   HANDLING.  35 

addition  of  culture.  This  tierce  was  put  down  as  a  check  on  tierce  1,  the  hams  being 
cured  under  exactly  the  same  conditions,  but  without  the  addition  of  culture  to  the 
curing  pickle. 

Result:  One  of  the  hams  which  was  pumped  in  the  shank  only  developed  slight 
souring  in  the  body.     The  remainder  of  the  hams  were  sweet. 

Comparing  tierce  1,  which  contained  the  inoculated  pickle,  with 
tierce  2,  the  check  tierce  which  contained  uninoculated  pickle,  we 
find  there  was  practically  no  difference  in  the  final  result.  In  tierce 
1  two  of  the  hams  developed  slight  souring,  while  in  tierce  2  one  of 
the  hams  became  slightly  sour.  All  of  these  hams  had  been  pumped 
in  the  shank' only.  The  fact  that  one  of  the  hams  in  the  check  tierce 
developed  slight  souring  was  undoubtedly  due  to  bacterial  contamina- 
tion in  pumping  or  in  the  handling  which  the  hams  underwent  prior 
to  pickling,  and  the  slight  souring  of  the  two  hams  in  tierce  1  must 
also  be  attributed  to  the  same  cause  or  causes,  for  had  the  souring 
in  these  last  hams  resulted  from  the  penetration  of  the  bacteria  from 
the  pickling  solution  a  higher  percentage  should  have  become  sour. 
Furthermore,  if  the  souring  of  the  two  hams  in  tierce  1  had  resulted 
from  the  penetration  of  the  bacteria  from  the  curing  pickle,  the  sour- 
ing should  have  been  general  throughout  the  bodies  of  these  hams, 
whereas  the  souring  was  only  evident  around  the  bone  and  was  slight 
in  degree. 

From  this  experiment  the  conclusion  would  seem  justified  that  the 
bacillus  which  causes  ham  souring  does  not  usually  find  its  way  into 
the  bodies  of  the  hams  from  the  curing  pickle,  although  it  would  be 
going  too  far,  perhaps,  to  say  that  infection  never  takes  place  from 
the  curing  pickle.  The  experiment,  however,  indicates  clearly  that 
the  curing  pickles  are  certainly  not  the  main  channel  through  which 
the  hams  become  infected.  In  referring  to  the  curing  pickles,  it 
should  be  understood  that  we  refer  here  to  the  pickling  solutions  in 
which  the  hams  are  immersed,  and  not  to  the  pumping  pickles.  The 
possibility  of  infection  through  the  pumping  pickle  will  be  discussed 
later. 

Possible  Infection  through  Manipulation  or  Handling. 

There  are  at  least  three  possible  ways  in  which  hams  may  become 
infected  from  the  handling  which  they  receive  in  preparation  for,  or 
during  the  process  of  curing,  viz:  From  the  thermometers  used  in 
taking  the  inside  temperatures  of  the  hams,  from  the  pumping 
needles,  and  from  the  billhooks  used  in  lifting  the  hams. 

infection  from  ham  thermometers. 

The  packing-house  method  of  taking  the  temperatures  of  hams  by 
means  of  a  pointed,  metal-capped  thermometer  which  is  thrust  deep 
into  the  bodies  of  the  hams  has  already  been  referred  to,  but  deserves 
to  be  described  somewhat  more  in  detail,  as  it  will  be  at  once  apparent 


36 


A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 


A. 


Fig.  4. — Diagrammatic 
views  showing  con- 
struction of  ham  ther- 
mometer. A,  front 
view,  showing  opwn 
space  between  metal 
point  and  mercury 
bulb,  which  becomes 
fllled  with  particles  of 
meat,  grease,  and 
dirt;  B,  side  view. 


that  this  manipulation  furnishes  a  ready  means 
whereby  hams  may  become  infected  with  putre- 
factive bacteria.  The  construction  of  a  ham  ther- 
mometer is  shown  in  figure  4.  . 

The  instrument  consists  of  a  glass  thermometer 
inclosed  in  a  metal  case,  the  front  portions  of  the 
case  being  cut  away  so  as  to  expose  the  scale  above 
and  the  mercury  bulb  below.  As  was  explained 
before,  the  thermometer  is  thrust  deep  into  the 
body  of  the  ham  so  that  the  pointed  end  contain- 
ing the  mercury  bulb  rests  beside  or  a  little  behind 
the  upper  portion  of  the  femur,  the  bone  being 
used  as  a  guide  in  introducing  the  thermometer. 

Ham  temperatures  are  taken  at  three  stages  in 
the  preparation  for  cure— ( 1)  on  the  hanging  floor, 
just  before  the  hams  go  to  the  chill  rooms,  in  order 
to  determine  the  amount  of  heat  lost  prior  to  chill- 
ing; (2)  on  leaving  the  chill  rooms,  in  order  to  de- 
termine the  thoroughness  of  the  chill;  (.3)  on  the 
packing  floor,  just  before  the  hams  are  placed  in 
pickle,  as  a  further  check  on  the  thoroughness  of 
the  chilling. 

In  taking  the  temperatures  of  hams  which  have 
been  chilled — and  most  of  the  temperatures  are 
taken  subsequent  to  chilling — it  is  customary  for 
the  packing-house  attendant  who  has  this  matter 
in  charge  to  warm  the  thermometer  by  holding  the 
pointed  or  bulb  end  in  his  hand,  so  as  to  force  the 
mercury  column  up  to  about  60°  F.,  or  well  above 
the  temperature  of  hams.  The  thermometer  is 
then  thrust  into  the  ham  and  allowed  to  remain 
for  several  minutes,  by  which  time  the  mercury 
column  will  have  fallen  to  the  temperature  of  the 
ham.  The  thermometer  is  then  slowly  withdrawn 
so  as  to  expose  the  top  of  the  mercury  column,  and 
an  accurate  reading  is  thus  obtained  of  the  inside 
temperature  of  the  ham.  The  thermometer  is 
warmed  by  the  hand  before  each  ham  is  tested,  and 
this  undoubtedly  insures  more  accurate  readings 
than  would  result  were  the  thermometer  removed 
from  one  ham  and  plunged  immediately  into 
another,  but  the  procedure  is  open  to  certain 
objections,  for  the  open  space  between  the 
metal  point  of  the  thermometer  and  the  mercury 


INFECTION   THROUGH    HAM   THERMOMETERS.  37 

bulb  soon  becomes  filled  with  particles  of  meat  and  with  grease  and 
dirt  from  the  attendant's  hands,  and  it  is  at  once  apparent  that  a 
thermometer  in  this  condition  would  furnish  a  ready  means  whereby 
extraneous  matter  might  be  introduced  into  the  bodies  of  the  hams. 
In  other  words,  a  contaminated  thermometer  would  furnish  an  excel- 
lent means  whereby  hams  could  be  inoculated  with  putrefactive 
bacteria. 

In  order  to  determine  whether  hams  actually  become  inoculated  in 
this  manner,  the  following  experiment  was  carried  out: 

EXPERIMENT    TO    SHOW    WHETHER     HAMS     BECOME     INFECTED     FROM     HAM    THERMOM- 
ETERS. 

This  experiment  was  designed  to  show  (1)  whether  the  usual 
packing-house  method  of  taking  ham  temperatures  was  apt  to  induce 
souring  in  the  hams  thus  tested,  and  (2)  whether  souring  would  result 
in  hams  which  were  tested  with  a  thermometer  purposely  contami- 
nated with  the  bacillus  isolated  from  sour  hams. 

The  experiment  was  carried  out  as  follows:  Thirty  hog  carcasses 
were  selected  as  they  entered  the  hanging  floor  from  the  killing  floor. 
They  had  been  cleaned,  eviscerated,  and  split,  and  were  of  the  same 
average  weight  and  of  sufficient  size  to  yield  hams  weighing  from  12 
to  14  pounds.  They  were  divided  into  three  lots  of  10  each  and  were 
allowed  to  remain  on  the  hanging  floor  for  two  hours,  after  which  they 
were  given  the  usual  48-hour  chilling. 

Lot  1. — The  hams  in  this  lot  were  tested  with  an  ordinary  ham  thermometer  as  they 
entered  the  hanging  floor,  as  they  left  the  hanging  floor,  and  as  they  left  the  coolers. 
The  thermometer  used  was  borrowed  from  one  of  the  plant  attendants  and  was  used  in 
the  condition  in  which  it  was  received  from  him;  that  is,  it  was  not  cleaned  or  disin- 
fected prior  to  use. 

Lot :?.— The  hams  in  this  lot  were  tested  as  they  entered  the  hanging  floor  with  a 
thermometer  which  had  been  previously  cleaned  and  disinfected  and  then  dipped  in 
a  culture  suspension  of  the  meat-souring  bacillus  which  was  isolated  from  sour  hams. 
The  thermometer  was  dipped  in  the  culture  suspension  before  each  ham  was  tested. 
No  further  temperatures  were  taken  of  these  hams.  The  thermometer  was  carefully 
cleaned  and  disinfected  before  it  was  returned  to  the  attendant  from  whom  it  was 
borrowed. 

Lot  3. — The  hams  in  this  lot  were  not  tested  at  all,  and  were  intended  as  checks  on 
the  cure. 

The  three  lots  of  carcasses  were  carefully  tagged  and  were  chilled  in 
a  special  cooler  to  themselves.  Upon  leaving  the  cooler  the  hams 
were  cut  from  the  carcasses  and  trimmed.  The  three  lots  of  hams 
were  then  cured  in  separate  tierces.  All  of  the  hams  were  subjected  to 
exactly  the  same  cure. 

The  pickles  used  were  the  regular  pumping  and  regular  curing 
pickles  of  the  establishment  at  which  the  experiment  was  carried  out. 


38 


A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 


The  hams  in  lot  3  were  pumped  first  and  those  in  lot  1  were 
pumped  next.  The  needle  was  then  removed  and  a  fresh,  clean 
needle  was  used  for  lot  2,  This  was  done  in  order  to  prevent  the 
possibility  of  carrying  over  bacteria  from  one  lot  of  hams  to  another 
on  the  pumping  needle.  The  tierces  were  thoroughly  cleaned  with 
boiling  water  before  being  used.  The  curing  was  carried  out  in  a 
pickling  cellar  which  was  held  at  33°  to  36°  F.,  the  temperature  never 
rising  above  the  latter  figure.  The  tierces  were  rolled  three  times 
during  the  curing.     The  details  and  results  were  as  follows: 

Tierce  /.—Contained  20  hams,  half  of  which  were  pumped  in  both  body  and  shank 
and  half  in  the  shank  only.  These  hams  were  taken  from  the  carcasses  in  lot  1  and  had 
been  tested  several  times  with  a  ham  thermometer,  as  already  described. 

Result:  At  the  end  of  the  cure  it  was  found  that  of  the  10  hams  which  were  pumped 
in  the  shank,  5  showed  well-marked  souring  in  the  body,  while  of  the  10  hams  which 
were  pumped  in  both  body  and  shank,  2  showed  slight  souring  in  the  body. 

Tierce  ^.—Contained  20  hams,  which  were  pumped  in  the  same  manner  as  those  in 
tierce  1.  These  hams  were  taken  from  the  carcasses  in  lot  2  and  had  been  tested  once 
with  a  thermometer  which  was  dipped  in  a  culture  suspension  of  the  bacillus  isolated 
from  sour  hams. 

Result:  The  10  hams  which  were  pumped  in  the  shank  only  all  became  sour.  When 
they  were  tried  out  at  the  end  of  the  cure,  they  showed  pronounced  souring  throughout 
the  entire  body  and  were  classed  as  "stinkers"  by  the  meat  inspector  who  examined 
them.  The  souring  extended  through  to  the  bone  marrow  of  the  femur  in  all  of  these 
hams.  Of  the  10  hams  which  were  pumped  in  both  body  and  shank,  7  showed 
well-marked  souring  in  the  body,  but  not  as  pronounced  as  in  those  pumped  in  the 
shank  only;  in  five  of  these  hams  the  souring  extended  through  to  the  bone  marrow  of 
the  femur,  while  in  2  the  bone  marrow  remained  sweet. 

Tierce  5.— Contained  20  hams,  which  were  pumped  in  the  same  manner  as  those  in 
the  two  preceding  tierces.  These  hams  were  not  tested  with  a  thermometer,  and  were 
put  down  as  a  check  on  the  cure.  They  were  pumped  with  the  same  pumping  pickle, 
subjected  to  the  same  cure,  and  held  under  precisely  the  same  conditions  as  the  hams 
in  the  two  preceding  tierces. 

Result:  When  tested  at  the  end  of  the  cure,  all  of  these  hams  were  found  to  be 
perfectly  sound  and  sweet. 

Results  of  experiment  to  show  whether  hams  become  infected  from  ham  thermometers. 


No.  of 
tierce. 

Number 
of  bams. 

Average 

weight  of 

hams. 

How  pumped. 

Treatment. 

Condition  at  end 
of  cure. 

Number 
of  sour 
hams. 

Percent- 
age of 
sour 
hams. 

20 

20 
20 

Pounds. 
12-14 

12-14 
12-14 

f  lOin  shank 

Tested  at  several  stages  in 
preparation  for  cure  with 
nam  thermometer  which 
had  not  been  cleaned. 
do 

5 

2 
10 

7 
0 

0 

1 

10  in  body  and  shanlc. . 

20 
100 

70 
0 

0 

lOinsbanlc 

Tested  once  with  ham  ther- 
mometer dipped  in  cul- 
ture suspension  of  ana- 
erobic   bacillus  isolated 
from  sour  hams. 
do 

2 

10  in  body  and  shank.. 

10  in  shank 

Not  tested  with  thermome- 
ter. 
do 

3 

10  in  body  and  shank. . 

RESULTS   OF   EXPERIMENT   WITH    HAM   THERMOMETERS.  39 

Several  hams  from  each  tierce  were  examined  bacteriologically. 
cultures  being  taken  from  the  meat  near  the  bone  and  from  the  bone 
marrow  of  the  femur. 

In  the  sour  hams  from  tierce  1  cultures  taken  from  the  meat  near 
the  bone  showed  the  same  anaerobic  bacillus  noted  in  other  sour 
hams  (i.  e.,  the  same  bacillus  which  caused  souring  in  Experiments  I 
and  II),  but  these  cultures  were  contaminated  with  other  bacteria 
which  were  probably  introduced  on  the  thermometer  along  with  the 
ham-souring  bacillus.  None  of  the  contaminating  bacteria  were 
capable,  however,  of  producing  a  sour-meat  odor  when  grown  on  the 
egg-pork  medium.  Pure  cultures  of  the  ham-souring  bacillus  were 
obtained  from  the  bone  marrow  of  some  of  these  hams,  showing  that 
this  bacillus  had  penetrated  through  to  the  bone  marrow  while  the 
other  bacteria  had  not. 

From  the  sour  hams  in  tierce  2  the  ham-souring  bacillus  was 
recovered  readily,  and  often  in  pure  culture,  from  the  hams  which 
had  been  pumped  in  the  shank  only,  whereas  it  was  usually  con- 
taminated with  pickle  bacteria  in  the  hams  which  had  been  pumped 
in  both  body  and  shank. 

In  the  case  of  the  sound  hams  in  tierce  3,  cultures  taken  from  the 
meat  near  the  bone  and  from  the  bone  marrow  of  the  femur  were 
negative  in  the  hams  which  had  been  pumped  in  the  shank  only, 
while  cultures  taken  from  corresponding  points  in  the  hams  pumped 
in  both  body  and  shank  showed  ordinary  pickle  bacteria,  which  had 
evidently  been  introduced  into  the  bodies  of  these  hams  in  the  pump- 
ing pickles.     None  of  these  hams  exhibited  the  slightest  sour  odor. 

Summary  of  experiment. — In  this  experiment  20  hams  (tierce  1) 
were  tested  with  an  ordinary  ham  thermometer  in  the  usual  packing- 
house manner.  Half  of  these  hams  were  subjected  to  the  mild  cure 
and  half  were  given  the  regular  cure,  with  the  result  that  50  per  cent 
of  those  receiving  the  mild  cure  and  20  per  cent  of  those  receiving  the 
regular  cure  became  sour. 

A  second  lot  of  20  hams  (tierce  2)  were  tested  with  a  thermometer 
which  had  been  purposely  contaminated  with  a  culture  suspension  of 
the  ham-souring  bacillus.  These  hams  were  cured  in  the  same  man- 
ner as  the  first  lot,  with  the  result  that  all  of  those  receiving  the  mild 
cure  and  70  per  cent  of  those  receiving  the  regular  cure  became  sour. 

A  third  lot  of  20  hams  (tierce  3)  which  had  not  been  tested  at  all 
were  cured  in  the  same  manner  as  the  two  preceding  lots,  as  a  check 
on  the  cure.     All  of  these  hams  were  sweet  at  the  end  of  the  cure. 

Inasmuch  as  the  three  lots  of  hams  were  cured  under  precisely  the 
same  conditions  and  were  handled  in  the  same  manner  prior  to  pick- 
ling, the  only  difference  being  that  t]ie  hams  in  tierces  1  and  2  were 
tested  with  the  ham  thermometer  while  those  in  tierce  3  were  not, 
we  must  conclude  that  the  souring  of  the  hams  in  tierces  1  and  2 


40  A   BACTERIOLOGICAL  STUDY   OF    HAM   SOURING. 

resulted  from  the  testing  which  these  hams  received.  In  the  case 
of  tierce  1  the  hams  became  infected  from  a  thermometer  which,  in 
the  ordinary  routine  use  of  the  packing  house,  had  become  acci- 
dentally contaminated  with  the  ham-souring  bacillus.  In  the  case 
of  tierce  2  the  hams  became  infected  from  a  thermometer  which 
had  been  artificially  contaminated  with  the  bacillus.  The  high 
percentage  of  sours  in  this  last  lot  is  due  to  the  fafct  that  these 
hams  were  heavily  infected  with  the  ham-souring  bacillus,  for  owing 
to  the  constmction  of  -the  ham  thermometer  many  thousands  of  the 
bacilli  were  unquestionably  introduced  into  each  ham  on  the  point 
of  the  thermometer.  In  the  ordinary  routine  of  ham  testing,  where 
hams  become  infected  from  foreign  matter  introduced  on  the  ther- 
mometer, the  percentage  of  souring,  as  shown  in  tierce  1,  would  be 
less,  for  it  is  not  to  be  supposed  that  ham  thermometers  are  always 
contaminated  with  the  ham-souring  bacillus,  but  that  they  only 
become  so  at  times,  and  that  probably  only  a  few  of  the  bacilli 
are  then  introduced. 

This  experiment,  w^e  think,  proves  conclusively  ( 1)  that  the  ham- 
souring  bacillus  may  be  introduced  into  the  bodies  of  hams  on  the 
thermometers  used  in  testing  the  hams,  and  (2)  that  the  packing- 
house method  of  taking  ham  temperatures  by  means  of  a  thermome- 
ter which  is  thrust  deep  into  the  bodies  of  the  hams  may  cause  sour- 
ing in  the  hams  thus  tested. 

As  a  further  proof  that  hams  may  become  contaminated  in  this 
manner,  a  series  of  cultures  were  made  from  scrapings  taken  from 
ham  thermometers.  The  scrapings  consisted  of  the  accumulations 
of  bits  of  meat,  grease,  and  dirt  that  collect  on  the  thermometers, 
and  were  taken  from  the  thermometers  while  the  latter  were  in 
ordinary  routine  use  in  the  packing  house.  In  a  series  of  sLx  cultures 
which  were  made  from  such  scrapings  at  different  times,  the  same 
bacillus  which  was  isolated  from  sour  hams  and  show  n  to  cause  meat 
souring  was  found  three  times.  In  other  words,  the  ham-souring 
bacillus  was  present  in  50  per  cent  of  the  cultures  made  from  ther- 
mometer scrapings,  and  many  hams  undoubtedly  become  infected 
from  the  thermometers.  Souring  would  be  almost  certain  to  result 
in  mild-cure  hams  if  these  hams  were  tested  with  a  thermometer 
which  had  become  accidentally  contaminated  with  the  ham-souring 
bacillus,  as  the  bacillus  would  have  time  to  develop  within  the  bodies 
of  the  hams  before  being  inhibited  by  the  curing  pickle,  which  pene- 
trates slowly  into  the  bodies  of  these  hams.  In  the  case  of  regular 
cure  hams— that  is,  hams  which  are  pumped  in  both  body  and  shank — 
souring  would  be  much  less  apt  to  occur  after  the  use  of  a  contami- 
nated thermometer,  as  these  hams  are  more  or  less  saturated  with  a 
strong  pumping  pickle  at  the  beginning  of  the  cure,  which  would 
tend  to  inhibit  the  growth  of  any  bacteria  that  might  be  introduced 
on  the  thermometers. 


INFECTION  FROM  PUMPING   NEEDLES.  41 

The  fact  that  souring  may  result  in  hams  from  the  use  of  a  contami- 
nated thermometer  would  explain  the  occurrence  of  several  sours  in 
one  vat,  for  in  testing  hams  just  before  they  go  into  cure  several  hams 
are  usually  tested  in  succession,  and  these  would  in  all  likelihood  go 
into  the  same  vat.  Supposing  the  thermometer  to  have  been  con- 
taminated with  the  ham-souring  bacillus  at  the  time  these  hams  were 
tested,  this  would  explain  a  fact  which  has  been  often  noted,  namely, 
the  occurrence  of  several  sours  in  one  vat  while  other  vats  containing 
the  same  run  of  hams  show  no  sours. 

If  souring  resulted  in  all  of  the  hams  which  are  subjected  to  a  ther- 
mometer test  in  the  daily  routine  of  the  packing  house,  this  manipu- 
lation alone  might  account  for  nearly  all  of  the  sours  which  occur,  but 
the  experiment  which  has  been  just  described  shows  that  all  of  these 
hams  do  not  become  sour.  In  tierce  1,  where  each  ham  was  subjected 
to  three  thermometer  tests  at  different  times,  souring  resulted  in  35 
per  cent  (this  includes  both  mild  and  regular  cure)  of  the  hams  thus 
tested,  and  in  actual  practice  the  percentage  of  sours  in  hams  which 
have  been  subjected  to  the  thermometer  test  would  probably  be 
somewhat  less.  Quite  a  large  percentage  of  sour  hams  are  thus  left 
unaccounted  for  by  the  thermometer  test,  and  we  believe  that  these 
are  chiefly  the  result  of  contamination  carried  in  on  the  pumping 
needles  or  in  the  pumping  pickles. 

INFECTION   FROM    PUMPING   NEEDLES. 

,  In  view  of  the  results  obtained  in  the  last  experiment,  in  which  it 
was  shown  that  hams  may  become  infected  from  the  use  of  ham  ther- 
mometers, it  seemed  not  improbable  that  hams  might  also  become 
infected  from  the  pumping  needles,  which,  like  the  thermometers, 
are  thrust  deep  into  the  bodies  of  the  hams  beside  the  bone.  In  order 
to  throw  some  light  upon  this  point,  cultures  were  taken  from  the 
grease  and  dirt  that  accumulate  on  the  shields  at  the  bases  of  the 
pumping  needles,  as  such  material  must  undoubtedly  be  carried  into 
the  hams  at  times  on  the  needles.  The  ham-souring  bacillus  was 
found  several  times  in  these  cultures,  and  hence  it  is  fair  to  infer  that 
hams  may  also  become  infected  at  times  from  the  pumping  needles, 
just  as  they  become  infected  from  the  thermometers.  Bits  of  con- 
taminated meat  and  grease  and  particles  of  dirt  carried  in  on  the 
pumping  needles  would  be  forced  out  into  the  hams  by  the  pumping 
pickle,  which  passes  out  through  small  openings  or  fenestras  in  the 
needles,  and  this  probably  affords  one  explanation  as  to  why  so  many 
more  body  sours  occur  in  the  mild-cure  hams.  In  the  mild-cure  hams, 
which  are  pumped  in  the  shank  only,  the  pumping  needle  is  intro- 
duced near  the  femorotibial  articulation,  and  the  shank  is  saturated 
at  the  start  with  a  strong  brine  solution,  while  the  body  of  the  ham  is 
not.     If  the  ham-souring  bacillus  were  carried  into  these  hams  on 


42  A  BACTERIOLOGICAL   STUDY  OF   HAM   SOURING. 

the  pumping  needle,  the  growth  of  the  bacillus  in  the  shank  would  be 
inhibited  by  the  strong  brine  solution  with  which  the  shank  is  satu- 
rated, but  there  would  be  nothing  to  prevent  the  bacillus  from  growing 
upward  into  the  body  of  the  ham,  which  has  not  been  pumped  and  is 
free  from  pickle.  This  would  also  explain  the  fact  that  the  souring 
often  starts  at  the  knee  joint  and  extends  upward  into  the  body  of 
the  ham.  In  the  case  of  the  regular  cure  hams,  where  the  ham  is 
pumped  in  both  body  and  shank,  the  entire  ham  is  more  or  less  satu- 
rated at  the  start  with  the  strong  brine  of  the  pumping  pickle,  which 
tends  to  inhibit  the  growth  of  the  ham-souring  bacillus  even  if  this 
bacillus  should  find  its  way  into  these  hams  on  the  pumping  needles. 
It  is  in  the  mild-cure  or  partly  pumped  hams,  where  the  body  of  the 
ham  is  left  unpumped,  that  the  ham-souring  bacillus  finds  its  best 
opportunity  for  development,  and  the  greater  proportion  of  the  sours 
that  occur  in  the  packing  house  are  found  in  these  hams. 

As  regards  the  possibility  of  infection  from  the  pumping  pickle 
itself,  it  does  not  seem  probable  that  this  would  often  occur,  for  the 
pumping  and  curing  pickles  are  always  prepared  on  an  upper  floor  of 
the  pickling  houses  and  are  delivered  to  the  pickle  cellars  in  closed 
pipes,  so  the  chances  for  the  accidental  contamination  of  these  solu- 
tions from  floating  dust  or  dirt  would  not  be  great.  Furthermore, 
the  strong  brine  of  the  pumping  pickle  would  completely  inhibit  the 
growth  of  the  ham-souring  bacillus,  and  the  bacillus  would  be  inca- 
pable of  multiplying,  even  if  it  found  its  way  into  the  pickle.  On  the 
other  hand,  laboratory  experiments  show  that  the  bacillus  or  its, 
spores  may  remain  alive  for  a  considerable  length  of  time  in  the  pump- 
ing pickle,  so  the  possibility  of  infection  from  this  source  can  not  be 
overlooked. 

INFECTION   FROM    BILLHOOKS. 

After  the  hams  are  cut  from  the  carcasses  they  are  handled  entirely 
by  means  of  billhooks.  In  handling  the  hams  the  hooks  are  inserted 
beneath  the  skin  of  the  shank  at  a  point  just  above  the  tibio-femoral 
articulation.  The  hooks  should  be  inserted  in  the  connective  tissue 
beneath  the  skin  and  should  not  penetrate  the  muscular  tissue  to 
any  depth.  When  the  hams  lie  in  the  right  position,  with  the  butt 
or  large  portion  away  from  and  the  shank  toward  the  operator,  it  is 
an  easy  matter  to  pick  them  up  in  the  proper  manner;  but  when 
they  lie  at  different  angles  and  are  being  rapidly  handled  it  is  almost 
impossible  to  prevent  the  hook  from  penetrating  the  muscular  tissues, 
and  if  the  hook  should  penetrate  to  the  bone  it  might  carry  in  foreign 
matter  contaminated  with  the  meat-souring  bacillus.  It  is  not  proba- 
ble that  many  hams  become  contaminated  in  this  way,  as  the  men 
who  handle  the  hams  are  very  skillful  in  manipulating  their  hooks; 
but  the  possibility  that  hams  may  become  contaminated  in  this 
manner  should  not  be  entirely  overlooked. 


CHARACTERISTICS   OF   THE    HAM-SOURING   BACILLUS.  43 

BIOLOGICAL    AND     MORPHOLOGICAL     CHARACTERISTICS     OF     THE     HAM- 
SOURING   BACILLUS. 

CONDITIONS   FAVORABLE   TO    GROWTH. 

The  most  favorable  medium  for  the  growth  of  the  organism  was 
found  to  be  the  modified  egg-meat  mixture  of  Rettger,  which  has 
been  previously  described.  In  this  medium  the  organism  develops 
rapidly  at  a  temperature  of  20°  to  25°  C,  giving  rise  to  the  character- 
istic sour-meat  odor.  Like  the  bacillus  described  by  Klein,  it  also 
grows  readily  on  pork -agar  and  pork -bouillon  containing  glucose, 
but  differs  from  Klein's  bacillus  in  that  it  will  grow,  though  less  luxu- 
riantly, on  ordinary  nutrient  media — agar,  gelatin,  and  bouillon — 
without  the  addition  of  glucose. 

The  optimum  temperature  for  growth  is  20°  to  25°  C.  The  organ- 
ism does  not  grow  at  incubator  temperature  (37.5°  C).  At  ice-box 
temperature  (8°  to  10°  C.)  it  develops  readily,  although  the  growth 
is  less  rapid  than  at  20°  to  25°  C.  That  the  organism  will  develop  at 
even  lower  temperatures  was  shown  in  the  inoculation  experiments 
with  hams,  where  it  developed  and  multiplied  extensively  in  the 
bodies  of  the  hams  at  the  temperature  of  the  pickling  cellars,  which 
are  held  usually  at  34°  to  36°  F.  (1°  to  2°  C). 

The  organism  develops  best  in  a  neutral  or  slightly  alkaline 
medium. 

GROWTH   ON   DIFFERENT   CULTURE    MEDIA. 

Growth  on  egg-'pork  medium. — At  a  temperature  of  20°  to  25°  C. 
the  cultures  show  a  sUght  but  distinct  sour  odor  in  from  two  to  three 
days.  This  odor,  as  before  stated,  closely  resembles  the  odor  of  a 
sour  ham.  Egg-pork  cultures  from  three  to  five  days  old  were  given 
to  a  trained  meat  inspector,  who  knew  nothing  whatever  as  to  the 
contents  of  the  tubes,  and  he  was  asked  to  describe  the  odor;  he 
described  it  as  that  of  a  sour  ham. 

At  one  week  the  albumins  of  the  medium  are  gelatinized  or  partly 
coagulated  and  the  odor  is  more  pronounced.  At  ten  days  the 
albumins  are  completely  coagulated  except  at  the  surface,  where 
there  is  no  apparent  growth;  the  odor  is  more  putrefactive  in  nature, 
and  the  reaction  of  the  medium  is  slightly  acid.  At  three  weeks  the 
coagulated  albumin  sphts  up  into  fragments  and  appears  to  undergo 
a  slow  digestion,  gas  bubbles  form  in  the  lower  portion  of  the  culture, 
and  the  odor  becomes  distinctly  putrefactive  in  character.  The  slow 
digestion  of  the  albumin  is  probably  due  to  a  proteolytic  enzym 
elaborated  by  the  bacillus. 

At  the  end  of  a  week  a  dark  zone  usually  appears  at  the  surface  of 
the  coagulated  albumin  and  gradually  darkens  until  it  becomes 
almost  black.  This  zone  is  probably  due  to  a  pigment  elaborated  by 
the  bacillus. 


44  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

At  ice-box  temperature  (8°  to  10°  C.)  the  same  changes  and  the 
same  odor  were  noted,  but  were  somewhat  slower  in  developing. 

Glucose-pork-agar. — This  medium  was  prepared  from  pork  in  the 
same  manner  as  beef-agar,  and  contained  1  per  cent  of  glucose.  The 
organism  grows  readily  on  this  medium  and  may  be  conveniently 
cultivated  in  deep  stab  cultures.  The  medium  was  always  thor- 
oughly boiled  and  then  rapidly  cooled  in  order  to  expel  the  inclosed 
air.  The  growth  of  the  organism  was  found  to  vary  considerably 
with  the  reaction. 

When  the  reaction  was  +  1.5,  deep  stab  cultures  at  three  days  (20° 
to  25°  C.)  showed  a  well-marked  aborescent  growth,  appearing  as 
delicate  filaments  extending  outward  from  the  hne  of  stab.  The 
growth  stopped  within  one-fourth  or  one-half  inch  of  the  surface  of 
the  agar  on  account  of  the  presence  of  oxygen  in  the  upper  part  of 
the  culture  medium.  As  the  growth  extended  toward  the  walls  of 
the  test  tube  the  agar  became  clouded,  and  there  were  sometimes  gas 
bubbles  in  the  depth  of  the  agar,  but  the  gas  formation  was  not 
extensive. 

When  the  reaction  of  the  agar  is  neutral  or  shghtly  alkaline,  exten- 
sive gas  formation  occurs  and  the  agar  is  often  much  broken  up. 

The  cultures  developed  a  disagreeable,  somewhat  putrefactive 
odor,  but  did  not  give  the  characteristic  sour-ham  odor  obtained  from 
the  egg-pork  cultures. 

The  organism  was  also  grown  on  anaerobic  agar  plates  by  Zinsser's 
method,  which  is  said  to  give  absolutely  anaerobic  conditions.  The 
colonies  on  agar  have  a  cottony  or  woolly  appearance  at  first,  and 
spread  slowly,  with  slightly  irregular  margins. 

In  glucose-pork-agar  to  which  azolitmin  was  added  the  azoHtmin 
in  the  lower  portion  of  deep  stab  cultures  was  completely  decolorized 
in  five  days  at  room  temperature  (20°  to  25°  C). 

In  glucose-pork-agar  containing  neutral  red  the  red  color  in  the 
lower  portion  of  the  tube  was  changed  to  yellow  with  the  develop- 
ment of  fluorescence. 

Neutral  gelatin. — Tubes  of  ordinary  neutral  gelatin  without  the 
addition  of  glucose  were  inoculated  and  held  at  ice-box  temperature 
(8°  to  10°  C).  At  five  days  a  dehcate  white  growth  appeared  along 
the  line  of  stab  in  the  lower  portion  of  the  tube.  At  seven  days  the 
growth  showed  finQ  radial  striae,  presenting  an  arborescent  or  tree- 
like appearance,  and  extended  halfway  from  the  line  of  stab  to  the 
walls  of  the  test  tube.  At  two  weeks  the  growth  had  caused  a  deli- 
cate clouding  of  the  medium  in  the  lower  portion  of  the  tube.  At 
three  weeks  the  gelatin  in  the  lower  portion  of  the  tube  had  become 
liquefied  and  the  growth  had  settled  to  the  bottom  as  a  white  pre- 
cipitate. 


GROWTH   OF  HAM-SOURING   BACILLUS  ON    CULTURE   MEDIA.       45 

In  gelatin  containing  glucose,  gas  bubbles  are  formed  in  the  depth 
of  the  medium  through  the  sphtting  up  of  the  glucose,  and  the 
characteristic  arborescent  growth  is  obscured. 

Glucose-porTc-houillon. — This  medium  was  prepared  from  pork 
instead  of  beef  and  contained  1  per  cent  of  glucose.  The  best  results 
were  obtained  when  the  reaction  of  the  medium  was  neutral  or 
slightly  alkaline. 

Culture  tubes,  which  had  been  previously  boiled  to  expel  the  con- 
tained air  and  then  inoculated,  were  held  in  a  Novy  jar,  in  an  atmos- 
phere of  hydrogen  at  a  temperature  of  20°  to  25°  C.  At  three  days 
the  tubes  showed  well-marked  clouding.  At  one  week  the  growth 
appeared  as  a  heavy,  white,  flocculent,  cottony  precipitate  in  the 
bottom  of  the  tubes  with  a  slight  flocculent  precipitate  above. 
When  the  culture  was  removed  from  the  jar  and  shaken,  the  heavy, 
flocculent  precipitate  at  the  bottom  of  the  tube  broke  up  without 
much  difficulty,  giving  rise  to  a  heavy  uniform  clouding  with  some 
small  floating  masses,  which  soon  settled  to  the  bottom.  On  shaking 
the  tube  some  evolution  of  gas  in  the  form  of  very  fine  bubbles  was 
noticed. 

In  Smith  fermentation  tubes  containing  neutral  glucose-pork-bou- 
illon the  closed  arm  of  the  tube  shows  well-marked  clouding  with  gas 
formation  at  three  days  at  room  temperature  (20°  to  25°  C).  The 
growth  has  a  tufted,  cottony  appearance,  and  there  are  many  iila- 
ments  and  threads.  The  growth  settles  to  the  bottom  of  the  closed 
arm  as  a  cottony,  white  precipitate  (see  PI.  IV).  The  organism 
splits  the  glucose  vigorously,  and  at  10  days  the  tubes  show  from 
40  to  50  per  cent  of  gas.  The  bouillon  in  the  open  arm  of  the  tube 
remains  unclouded.  The  maximum  gas  production  at  room  tempera- 
ture is  reached  in  from  10  to  14  days,  by  which  time  the  growth  in  the 
closed  arm  has  completely  settled  into  the  bend  of  the  tube,  leaving 
the  bouillon  in  the  closed  arm  clear.     The  gas  formula,  as  determined' 

H       5 
by  Smith's  method,  was  p/^  = ,  •    The  reaction  of  the  bouillon  becomes 

acid  to  phenolphthalein. 

The  organism  will  grow  on  ordinary  neutral  bouillon  without  the 
addition  of  glucose,  and  in  Smith  tubes  containing  this  medium  a 
small  amount  of  gas  was  formed,  due  to  the  splitting  of  the  muscle 
sugar. 

The  bacillus  also  grows  in  a  sugar-free  broth — that  is,  a  broth  free 
from  muscle  sugar — and  from  cultures  grown  in  this  medium  a  well- 
marked  indol  test  was  obtained. 

Litmus-milk. — The  organism  was  grown  in  litmus-milk  in  Smith 
fermentation  tubes  at  20^  to  25°  C.  At  seven  days  the  litmus  in  the 
lower  portion  of  the  closed  arm  had  assumed  a  brownish-buff  color. 
At  two  weeks  the  litmus  in  the  closed  arm  had  been  reduced  to  a 


46 


A   BACTERIOLOGICAL   STUDY   OF   HAM   SOURING. 


brownish-buff  color  except  at  the  top  of  the  tube,  where  a  pale, 
bluish  tinge  remained,  and  the  litmus  in  the  open  arm  showed  very 
slight  reddening  as  compared  with  a  check  tube.  At  three  weeks  the 
litmus  in  the  closed  arm  was  entirely  reduced  to  a  light,  brownish- 
buff  color,  and  the  litmus  in  the  open  arm  showed  a  slight  but  dis- 
tinct reddening  as  compared  with  the  check.  The  reddening  of  the 
litmus  in  the  open  arm  was  evidently  due  to  the  transfusion  of  acids 
formed  bj''  the  growth  of  the  bacillus  in  the  closed  arm.  After  sev- 
eral weeks  the  milk 
is  slowly  peptonized, 
probably  as  a  result 
of  enzym  action. 

MORPHOLOGY. 

The  organism  is  a 
large  bacillus  having 
an  average  size  of  4 
to  8 ,« in  length  by  0 . 5 
to  O.l/iin  thickness, 
but  there  are  many 
longer  forms  meas- 
uring from  10  to  20 
/£  in  length.  It  de- 
velops in  long,  ir- 
regular chains  or 
filaments,  which  at 
times  show  a  slightly 
spiral  form. 

The  individual 
organisms  show  at 
times  a  widely  open,  slightly  spiral  form,  which  was  more  apparent  in 
hanging-drop  preparations  made  from  bouillon  cultures,  where  the 
organisms  had  been  comparatively  undisturbed.  This  appearance  was 
also  noted  at  times  in  the  stained  sections  of  soured  muscular  tissue, 
where  the  organisms  were  stained  in  place.  The  organism  possesses 
no  motility.  It  stains  with  the  ordinary  aniline  dyes  and  by  Gram's 
method. 

SPORE    FORMATION. 

The  organism  develops  large,  terminal  spores,  which  are  at  first 
oval,  but  when  fully  developed  are  perfectly  round  and  measure 
from  1.5  to  2  /x  in  diameter. 

Spores  develop  rapidly  in  the  egg-pork  medium  at  20°  to  25°  C, 
fully  developed  spores  being  noted  in  from  five  to  seven  days.     At 


Fig.  5.— Ham-souring  bacillus  (^Bacilln^  putrefaciens)  grown  on  egg-pork 
medium,  showing  tendency  to  form  chains.  Partly  developed  and 
fully  developed  spores  are  shown  at  ends  of  rods;  also  free  spores. 
(Pen-and-ink  drawing  made  with  camera  lucida  from  preparation 
stained  by  Gram's  method.    X  <140.) 


RESISTANCE   OF   BACILLUS   TO   HEAT,  ETC.  47 

ice-box  temperature  (8°  to  10°  C.)  partly  developed  spores  were 
noted  in  the  egg-pork  medium  at  10  days  and  fully  developed 
spores  at  2  weeks. 

Occasional  spores'  were  noted  in  old  agar  and  gelatin  cultures, 
but  abundant  spore  formation  was  seen  only  in  the  egg-pork  medium. 
No  spores  were  noted  in  bouillon  cultures,  even  at  10  weeks. 

RESISTANCE    TO    HEAT   AND    CHEMICAL   AGENTS. 

In  its  vegetative  form  the  bacillus  is  killed  at  55°  C.  in  10  minutes. 
The  spores  survive  a  temperature  of  80°  C.  for  20  minutes,  but  are 
killed  at  100°  C.  in  10  minutes. 

When  sodium  chlorid  and  potassium  nitrate  were  added  to  glu- 
cose-pork broth  in  varying  amounts,  it  was  found  that  3  per  cent  of 
sodium  chlorid  or  3  per  cent  of  potassium  nitrate  was  sufficient  to 
inhibit  completely  the  growth  of  the  bacillus  at  room  temperature 
(20°  to  25°  C). 

While  the  growth  of  the  bacillus  was  inhibited  by  sodium  chlorid 
and  potassium  nitrate  as  just  stated,  it  was  found  that  very  much 
stronger  solutions  of  the  two  salts  failed  to  destroy  the  bacillus. 
Thus  it  was  found  that  the  bacillus  or  its  spores  retained  their  vitality 
after  an  exposure  of  30  days  in  a  solution  containing  23  per  cent  of 
sodium  chlorid  and  6  per  cent  of  potassium  nitrate. 

GAS    PRODUCTION. 

The  organism  splits  glucose,  but  not  lactose  or  saccharose.  That 
it  possesses  the  power  of  splitting  muscle  sugar  was  shown  by  the 
formation  of  gas  in  Smith  fermentation  tubes  containing  ordinary 
neutral  bouillon  without  the  addition  of  any  sugar. 

The  formation  of  gas  in  glucose  bouillon  varies  considerably  vnth 
the  reaction  of  the  medium.  The  largest  amount  of  gas  was  formed 
when  the  broth  was  neutral  or  slightly  alkaline.  When  the  reaction 
of  the  broth  was  distinctly  acid  or  distinctly  alkaline  the  amount 
of  gas  was  diminished.  The  gas  which  is  formed  in  bouillon  cultures 
consists  chiefly  of  hydrogen  and  carbon  dioxid.  In  order  to  collect 
a  sufficient  amount  of  the  gas  for  analysis,  two  large  fermentation 
tubes  capable  of  holding  150  cubic  centimeters  each  were  con- 
structed. These  tubes  were  filled  with  pork-bouillon  and  inoculated 
with  the  bacillus.  After  20  days  at  room  temperature  (20°  to  25°  C.) 
the  gas  was  collected  and  the  carbon  dioxid  and  hydrogen  deter- 
mined, with  the  following  result: 

Cubic  centimeters. 

Total  amount  of  gas  collected 37.  7 

Carbon  dioxid,  by  absorption  with  NaOH 6.  2 

Hydrogen,  by  difference 31.5 

This  analysis  gives  an  approximate  gas  formula  of  pTv  =  t,    which 

agrees  with  the  gas  formula  as  determined  in  the  small  fermentation 
tubes  by  Smith's  method. 


48 


A  BACTERIOLOGICAL  STUDY   OF    HAM   SOURING. 


In  hams  which  had  undergone  spontaneous  souring  and  in  hams 
which  had  been  artificially  soured  by  inoculation,  hydrogen-sul- 
phid  was  often  noted  when  the  sour  portions  of  the  meat  were  tested 
with  lead-acetate  paper,  but  no  distinct  odor  of  the  gas  could  be 
obtained.  Hydrogen  sulphid  was  also  noted  in  egg-pork  cultures  of 
the  bacillus. 


ACID   PRODUCTION. 


In  glucose-bouillon,  butyric  and  lactic  acids  are  formed  and  the 
reaction  of  the  medium  becomes  distinctly  acid.  Butyric  and  lactic 
acids  were  also  noted  in  the  egg-pork  cultures. 

A  series  of  Smith  fermentation  tubes  containing  10  c.  c.  each  of 

glucose-pork  broth  medium  was  inoculated   with  the  bacillus  and 

held  at  room  temperature   (20°    to  25°   C).     These  cultures    were 

N 
titrated  against  — NaOH,  with  phenolphthalein  as  an  indicator  at 

intervals  of  two  days  up  to  nineteen  days,  and  then  at  two-week 
intervals  up  to  sixty-one  days.  •  Three  of  the  cultures  were  titrated 
each  time  so  as  to  give  a  fair  average  of  the  acidity  of  the  cultures, 
and  an  uninoculated  check  tube  was  also  titrated  each  time  to  see 
if  there  was  any  change  in  the  reaction  of  the  medium.  The  results 
of  the  titrations  are  shown  in  the  following  table : 

Acidity  determinations  in  glucose-pork  broth  cultures. 


Age  of  culture  (days). 

Culture  A. 

Culture  B. 

Culture  C. 

Average. 

Medium. 

Acidity  of 
culture. 

■2 

0. 038 
.105 
.106 
.124 
.128 
.129 
.126 
.125 
.122 
.121 

0.030 
.100 
.110 
.115 
.130 
.120 
.125 
.123 
.120 
.116 

0.040 
.102 
.109 
.117 
.126 
.129 
.125 
.125 
.121 
.119 

0.036 
.102 
.108 
.119 
.128 
.126 
.125 
.124 
.121 
.118 

0.009 
.009 
.009 
.009 

..009 
.009 
.009 
.009 
.009 
.009 

Per  cent. 
0.027 

4                           

.093 

6                  

.099 

8     

.110 

10 

.119 

12 

.117 

19              

.116 

33".   

.115 

47 

.112 

61                               

.109 

From  the  above  table  it  will  be  seen  that  the  maximum  acidity 
was  reached  at  ten  days,  after  which  there  was  a  gradual  reduction 
in  the  acidity,  due  probably  to  the  formation  of  ammonia  compounds. 


PATHOGENIC   PROPERTIES. 


Rabbits,  guinea  pigs,  and  white  mice  were  inoculated  and  fed  with 
cultures  of  the  bacillus  without  effect,  from  which  it  would  appear 
that  the  bacillus  possesses  no  pathogenic  or  disease  -  producing 
properties. 


NATURE    OF   THE    BACILLUS. 


The  bacillus  is  essentially  a  saprogenic  bacterium  with  zymogenic 
properties.     A  preliminary  study  of  the  chemical  changes  which  take 


BuL.  132,  Bureau  of  Animal  Industry,  U.  S.  Dept.  of  Agriculture. 


Plate  IV. 


i  ■  'i 

Jiec;^^ 

^^'Li^^H 

m 

c  'W^' 

\ 

y 

m 

^-a-:i.j«L.- 

Glucose  Bouillon  Culture  in  Smith  Fermentation  Tube  at  Four 
Days.  Culture  Grown  at  Room  Temperature  (20°  to  25°  C). 
Growth  Confined  Entirely  to  Closed  Arm,  with  Gas  Col- 
lecting AT  Top. 


I 


i* 


NATURE   OF   THE   BACILLUS.  49 

place  in  sour  hams  shows  that  these  changes  are  of  a  putrefactive 
nature.  Hams  which  had  undergone  spontaneous  souring  were  com- 
pared with  hams  which  had  been  artificially  soured  by  inoculation, 
and  the  chemical  changes  were  found  to  be  identical.  A  chemical 
study  was  also  made  of  the  changes  taking  place  in  egg-pork  cultures 
of  the  bacillus  at  different  stages  of  growth,  and  these  changes  were 
found  to  be  of  a  putrefactive  nature  and  similar  in  character  to  the 
changes  which  occur  in  sour  hams.  Among  the  putrefactive  products 
formed  by  the  growth  of  the  bacillus  in  the  egg-pork  medium  were 
indol,  skatol,  volatile  fatty  acids,  skatol-carbonic  acid,  and  hydrogen 
sulphid.^ 

A  more  extended  study  is  now  being  carried  on  in  the  Biochemic 
Division  of  the  chemical  changes  which  take  place  in  hams  during 
the  process  of  souring,  together  with  a  further  study  of  the  chemical 
changes  which  result  from  the  growth  of  the  bacillus  in  the  egg-pork 
medium.  The  results  of  this  investigation  will  be  given  in  a  later 
paper. 

The  bacillus  described  in  this  paper  belongs  to  the  class  of  putre- 
factive anaerobes,  which  are  widely  distributed  in  nature  in  dust,  soil, 
and  excrementitious  matters.  This  group  of  bacteria  contains  both 
pathogenic  and  nonpathogenic  forms.  The  former  have  received 
considerable  attention,  but  the  latter  hp,ve  never  been  thoroughly 
cleared  up.  The  bacillus  isolated  from  sour  hams  belongs  in  the  latter 
category,  being  possessed  of  no  pathogenic  or  disease-producing  prop- 
erties. It  occurs  in  the  dust  and  dirt  of  the  packing  house  and  finds 
its  way  into  the  hams  in  the  various  manipulations  to  which  the  hams 
are  subjected. 

The  bacillus  described  in  this  paper  does  not  seem  to  correspond 
with  any  forms  heretofore  described.  It  differs  from  Klein's  bacillus 
{Bacillus  foedans)  in  the  following  important  particulars:  (1)  It  forms 
large  terminal  spores,  whereas  Klein's  bacillus  formed  no  spores;  (2)  it 
will  grow  at  a  temperature  of  34°  F.,  while  Klein's  bacillus  did  not  grow 
below  50°  F.;  (3)  it  produces  an  acid  reaction  in  culture  media,  while 
Klein's  bacillus  gave  a  distinctly  alkaline  reaction;  (4)  it  will  grow  on 
the  ordinary  nutrient  media — gelatin,  agar,  and  broth — without  the 
addition  of  glucose,  while  Klein's  bacillus  did  not;  (5)  it  peptonizes 
the  casein  in  milk,  whereas  Klein's  bacillus  had  no  action  on  milk; 
(6)  it  liquefies  gelatin  more  rapidly,  causing  complete  liquefaction 
after  three  weeks  at  8°  to  10°  C,  whereas  Klein's  bacillus  caused  only 
partial  liquefaction  after  eight  weeks  at  20°  C. ;  (7)  it  can  be  conveyed 

>  The  tests  for  the  putrefactive  products  formed  by  the  growth  of  the  bacillus  in  the  egg-pork  medium 
were  made  by  P.  Castleman,  of  the  Biochemic  Division,  who  also  determined  the  percentage  compositioa 
of  the  gas  formed  by  the  growth  of  the  bacillus  in  the  glucose-pork-bouillon  medium. 


50  A  BACTEEIOLOGICAL  STUDY   OF   HAM   SOURING. 

from  turbid  broth  cultures  to  new  culture  material  by  means  of  the 
platinum  loop,  whereas  Klein's  bacillus  could  not  be  thus  conveyed. 
For  the  bacillus  described  in  the  present  paper  the  following  name 
is  proposed:  Bacillus  putrefaciens. 

PREVENTION  OF  HAM  SOURING. 

As  it  has  been  shown  that  souring  in  hams  results  from  the  growth 
of  a  bacterium  which  is  introduced  into  the  bodies  of  the  hams  in  the 
various  manipulations  which  the  hams  undergo,  the  only  way  to  elimi- 
nate souring  in  hams,  as  they  are  cured  in  the  larger  packing  estab- 
lishments, would  be  to  cure  the  hams  under  aseptic  or  sterile  condi- 
tions, which  would,  of  course,  be  a  physical  impossibility. 

While  it  will  probably  be  impossible,  therefore,  to  eliminate  souring 
entirely  under  the  methods  of  ham  curing  which  are  at  present  em- 
ployed in  the  larger  packing  establishments,  much  can  undoubtedly 
be  done  toward  reducing  the  percentage  of  sours.  In  the  matter  of 
taking  ham  temperatures,  for  instance,  if  the  thermometers  used  were 
thoroughly  cleaned  and  disinfected  and  the  surfaces  of  the  hams 
seared  at  the  point  where  the  thermometer  is  introduced,  infection 
from  this  source  could  be  entirely  prevented ;  or  it  might  be  possible 
so  to  regulate  the  temperature  of  the  chill  rooms  that  the  taking  of 
ham  temperatures  could  be  discontinued. 

The  elimination  of  the  souring  that  results  from  the  introduction 
of  foreign  matter  on  the  pumping  needles  could  be  effected  in  two 
ways  only,  (1)  by  not  pumping  the  hams  at  all,  or  (2)  by  pumping 
them  under  sterile  or  aseptic  conditions.  As  has  been  stated  before, 
some  of  the  smaller  packing  establishments  cure  their  hams  without 
pumping,  and  in  these  establishments  the  percentage  of  sours  runs 
very  low.  When  hams  are  cured  without  pumping,  however,  the 
period  of  curing  has  to  be  materially  lengthened  in  order  to  give  the 
curing  pickles  sufficient  time  to  penetrate  thoroughly,  and  this  is 
what  the  larger  plants  wish  to  avoid  because  of  the  greater  space  and 
greater  number  of  vats  which  would  be  necessitated.  The  object  of 
pumping  in  the  larger  plants,  where  the  number  of  hams  handled 
daily  runs  into  the  thousands,  is  to  hasten  the  cure  and  thus  pre- 
vent the  accumulation  of  a  great  number  of  hams  at  one  time.  It  is 
doubtful,  therefore,  whether  the  larger  packing  houses  could  con- 
veniently discontinue  pumping. 

To  pump  the  hams  under  aseptic  conditions  would  necessitate  a 
technique  far  too  elaborate  for  routine  use  in  the  packing  house;  in 
fact,  anything  like  complete  asepsis  would  be  out  of  the  question. 
Certain  measures  might  be  adopted,  however,  that  would  tend  to 
prevent  the  possible  introduction  of  ham-souring  bacilli  in  the  proc- 
ess of  pumping.  It  would  undoubtedly  be  safer,  for  instance,  to 
boil  the  pumping  pickle  before  use,  and  the  chances  of  carrying  in 


PREVENTION   OF   HAM   SOUKING.  51 

contaminated  foreign  matter  on  the  pumping  needles  could  be  lessened 
by  sterilizing  the  pumps  and  needles  with  boihng  water  and  by  fre- 
quently dipping  the  needles,  while  in  use,  in  boiling  water.  If  the 
hams  were  sprayed  with  clean  water  just  "prior  to  pumping,  there 
would  be  less  likelihood  of  carrying  in  foreign  matter  on  the  needles. 
The  danger  of  introducing  contaminated  foreign  matter  on  the  nee- 
dles might  be  further  obviated  by  searing  the  surfaces  of  the  hams  at 
the  points  where  the  needles  are  introduced;  but  such  a  procedure 
would  be  hardly  practicable  in  the  larger  packing  houses,  where  the 
great  number  of  hams  cured  necessitates  rapid  handling. 

While  the  danger  of  possible  contamination  in  pumping,  through 
the  introduction  of  contaminated  foreign  matter  on  the  pumping 
needles,  can  not  well  be  avoided,  this  danger  is  partly  counterbal- 
anced by  the  inhibitory  action  of  the  pumping  pickle,  which  is  strik- 
ingly shown  in  the  experiments  which  have  been  described.  In  these 
experiments,  100  hams  received  large  doses  of  the  ham-souring  bacillus, 
half  of  these  hams  being  subjected  to  the  mild  cure  and  half  to  the 
regular  cure,  with  the  following  result:  In  the  case  of  the  mild- 
cure  hams,  which  were  pumped  in  the  shank  only,  the  percentage 
of  sours  was  practically  100  per  cent,  everj'  ham  with  possibly  one 
exception  becoming  sour;  whereas  in  the  regular-cure  hams,  which 
were  pumped  in  both  body  and  shank,  only  58  per  cent  of  the  hams 
became  sour.  In  other  words,  the  additional  pumping  which  the 
regular-cure  hams  received  served  to  prevent  souring  in  42  per  cent 
of  these  hams.  In  these  experiments  the  number  of  bacteria  intro- 
duced into  the  hams  was  very  great,  thousands  and  even  millions  of 
the  bacilli  being  introduced  into  each  ham,  whereas  in  the  routine  of 
the  packing  house  it  is  not  likely  that  more  than  a  few  of  the  bacilli 
are  ever  introduced  at  one  time  on  the  thermometers  and  pumping 
needles.  In  view  of  these  results  it  is  safe  to  say  that  in  the  larger 
packing  houses,  where  pumping  seems  to  be  necessary,  the  number 
of  sours  could  be  reduced  fully  50  per  cent  if  all  hams  were  pumped  in 
the  body  as  well  as  in  the  shank. 

At  present  the  usual  procedure  is  to  pump  all  hams,  both  mild  and 
regular  cure,  with  the  same  pumping  pickle,  the  mild-cure  hams 
being  pumped  in  the  shank  only  and  the  regular-cure  hams  at  two 
additional  points  in  the  body.  The  experiments  quoted  above 
show  that  the  additional  pumping  which  the  regular-cure  hams 
receive  undoubtedly  tends  to  prevent  the  development  of  souring 
in  these  hams,  and  this  result  is  unquestionably  due  to  the  inhibitory 
action  of  the  salts  contained  in  the  pumping  pickle,  as  it  was  found 
by  laboratory  experiment  that  the  addition  of  3  per  cent  of  sodium 
chlorid  to  culture  media  is  sufficient  to  inhibit  the  growth  of  the 
ham-souring  bacillus.  The  pumping  pickles  consist  of  strong  brine 
solutions  and  always  contain  considerably  more  than  3  per  cent  of 


52  A  BACTERIOLOGICAL  STUDY  OF   HAM   SOURING. 

sodium  clilorid.  If,  therefore,  the  pumping  of  regular-cure  hams 
were  made  more  thorough  than  at  present,  and  all  of  the  deeper  por- 
tions of  the  ham  were  thoroughly  saturated  with  the  strong  brine 
solution,  souring  could  be  largely  eUminated,  if  not  entirely  prevented, 
in  these  hams,  as  an  unfavorable  medium  or  soil  would  thus  be 
created  in  which  the  ham-souring  bacillus  could  not  develop.  The 
ham-souring  bacillus  is  able  to  develop  within  the  bodies  of  the 
regular-cure  hams  because  the  pumping  of  these  hams  is  not  always 
thorough  and  there  are  certain  areas  in  the  inner  or  deeper  portions 
of  the  hams  in  which  the  tissues  are  not  thoroughly  saturated  with 
the  pumping  pickle. 

Under  the  present  methods  of  curing,  the  greater  proportion  of 
the  sours  occur  among  the  partly  pumped  or  mild-cure  hams.  These 
hams  are  pumped  in  the  shank  only,  and  the  growth  of  the  ham- 
souring  bacillus  within  the  bodies  of  these  hams  is  not  interfered 
with  until  the  curing  pickle  has  penetrated  from  the  outside.  As 
it  requires  several  weeks  for  the  curing  pickle  to  penetrate  thor- 
oughly into  the  deeper  portions  of  these  hams,  the  bacillus  is  thus 
afforded  a  considerable  interval  in  which  to  develop  before  it  is 
exposed  to  the  inhibitorv'  action  of  the  pickle.  If  these  hams 
could  be  thoroughly  pumped  in  the  body  at  the  beginning  of  the  cure 
in  the  same  manner  as  the  regular-cure  hams,  the  cliief  loss  from 
ham  souring  would  be  eliminated.  It  would  not  do,  however,  to 
pump  these  hams  in  the  body  with  the  same  pumping  pickle  used  in 
the  regular  cure,  as  the  meat  would  be  rendered  too  salty  and  the 
mild  flavor  of  the  ham  would  be  lost.  There  is  undoubtedly  a  demand 
for  mild-cure  hams,  otherwise  they  would  not  be  on  the  market;  and 
the  question  then  arises  how  to  pump  these  hams  and  still  retain  a 
mild  cure.  This  might  be  accomplished  by  pumping  these  hams 
with  their  own  curing  pickle,  which  is  usually  a  milder  pickle  than 
that  employed  in  the  regular  cure,  or  an  even  milder  pumping  pickle 
might  be  used.  If  mild-cure  hams  were  pumped  in  this  way,  the 
percentage  of  souring  in  these  hams  could  undoubtedly  be  greatly 
diminished  without  materially  affecting  the  flavor  of  the  ham. 

To  recapitulate  briefly,  the  prevention  of  ham  souring  is  to  be 
sought  in  two  ways:  (1)  Through  greater  care  in  handling  the 
hams  and  the  adoption  of  precautionarj'  measures  to  prevent  the  in- 
troduction of  the  ham-souring  bacillus  into  the  bodies  of  the  hams, 
and  (2)  tlirough  more  thorough  pumping  of  the  deeper  or  inner  por- 
tions of  the  hams,  so  as  to  create  an  unfavorable  soil  or  medium  in 
which  the  ham-souring  bacillus  can  not  develop  even  if  it  should 
gain  entrance  into  the  bodies  of  the  hams. 

From  what  has  been  said  it  will  be  apparent  that  ham  souring 
can  probably  never  be  entirely  eliminated  from  the  packing  house 
under  the  present  methods  of  curing,  but  the  adoption  of  precaution- 


SUMMARY  AND   CONCLUSIONS.  53 

aiy  measures  in  testing  and  pumping  hams,  together  with  a  more 
thorough  pumping  of  all  hams  in  ways  similar  to  those  suggested, 
would  unquestionably  reduce  very  materially  the  losses  from  this 
source. 

GENERAL  SUMMARY  AND  CONCLUSIONS. 

1.  In  this  paper  it  has  been  shown  that  ham  souring,  as  encountered 
in  the  wet  cure  where  the  hams  are  entirely  submerged  in  pickling 
fluids,  is  due  to  the  growth  of  an  anaerobic  bacillus  within  the  bodies  of 
the  hams.  This  bacillus  {B.  putrefaciens)  was  found  in  sour  hams 
obtained  from  four  different  packing  establishments.  It  was  isolated 
and  grown  in  various  laboratory  media,  in  one  of  which,  the  egg- 
pork  medium,  it  gave  rise  to  the  characteristic  sour-ham  odor. 
This  bacillus  was  the  only  organism  that  could  be  isolated  from  sour 
hams  that  was  capable  of  producing  the  characteristic  sour-ham  odor 
in  the  egg-pork  medium. 

2.  When  injected  into  the  bodies  of  sound  hams,  the  bacillus 
caused  these  hams  to  sour  in  the  process  of  curing.  In  hams  which 
had  been  inoculated  with  the  bacillus  and  thus  artificially  soured,  the 
bacillus  was  recovered  in  cultures  taken  at  points  far  removed, 
relatively  speaking,  from  the  point  of  inoculation,  indicating  that 
the  bacillus  had  multiplied  and  progressed  by  extension  throughout 
the  bodies  of  the  hams. 

3.  The  bacillus  possesses  no  motility,  and  its  extension  throughout 
the  bodies  of  the  hams  is  a  result  of  multiplication.  In  its  growth 
it  follows  along  the  connective-tissue  bands  between  the  muscle 
bundles,  which  are  composed  of  comparatively  loose  tissue  and 
afford  paths  of  least  resistance.  When  it  invades  the  muscle  tissue 
proper,  it  follows  along  the  sarcolemma  sheaths  between  the  muscle 
fibers.  As  a  result  of  this  growth  the  muscular  tissue  becomes  softer 
and  tends  to  break  more  easily, 

4.  The  bacillus  belongs  to  the  class  of  putrefactive  anaerobes 
which  are  widely  distributed  in  nature  in  dust,  soil,  and  excrementi- 
tious  matters.  The  bacillus  or  its  spores  is  present  in  the  dust  and 
dirt  of  packing  houses  and  finds  its  way  into  the  hams  in  the  various 
manipulations  to  which  they  are  subjected. 

5.  The  bacillus  or  its  spores  may  be  introduced  into  hams  on  the 
thermometers  used  in  testing  the  hams,  on  the  pumping  needles, 
and  possibly  on  the  billhooks  used  in  handling  the  hams.  It  may 
also  be  carried  into  the  hams  in  the  pumping  pickle,  and  may  even 
find  its  way  into  the  hams  from  the  curing  pickle,  although  infection 
through  the  latter  channel  probably  does  not  often  occur. 

6.  The  bacillus  develops  in  the  deeper  portions  of  the  ham  because 
of  the  anaerobic  conditions  there  prevailing,  and  souring  is  most 
often  encountered,  therefore,  in  the  deeper  portions  of  the  ham 
near  the  bone. 


54  A   BACTERIOLOGICAL  STUDY   OF    HAM   SOURING. 

7.  A  preliminary  study  of  the  chemical  changes  which  take  place 
in  the  process  of  souring  shows  that  these  changes  are  of  a  putre- 
factive nature,  and  ham  souring,  as  ordinarily  encountered,  is  to  be 
regarded  as  an  incipient  putrefaction.  Hams  which  had  been 
artificially  soured  by  injections  of  culture  were  compared  with  sour 
hams  obtained  from  the  packing  house,  and  the  putrefactive  changes 
were  found  to  be  identical. 

8.  Hams  which  have  once  become  sour  can  never  be  restored  to  a 
sound  condition,  because  of  the  chemical  changes  which  result  from 
the  growth  of  the  bacillus.  In  other  words,  the  tissues  of  the  ham 
undergo  certain  chemical  changes  in  the  process  of  souring,  and 
when  these  changes  have  once  taken  place  the  tissues  can  never  be 
restored  to  a  sound  condition.  The  repumping  of  slightly  soured 
hams  with  a  strong  pumping  pickle  will  check  further  souring,  by 
inhibiting  the  growth  of  the  bacillus,  but  will  not  restore  to  a  sound 
condition  those  portions  of  the  ham  which  have  become  sour. 

9.  The  salts  of  the  pickling  fluids  have  a  marked  inhibitory  action 
on  the  ham-souring  bacillus,  and  sours  occur  less  frequently  in  regular- 
cure  hams. 

10.  In  regular-cure  hams  the  growth  of  the  ham-souring  bacillus 
is  restricted  and  often  completely  inhibited  as  a  result  of  the  addi- 
tional pumping  which  these  hams  receive,  whereby  they  are  more 
or  less  saturated  with  pickle  at  the  beginning  of  the  cure. 

11 .  If  the  pumping  of  regular-cure  hams  were  more  thorough  and 
all  of  the  deeper  portions  of  the  ham  were  thoroughly  saturated 
with  the  pumping  pickle,  souring  could  be  largely  eliminated  if  not 
entirely  prevented  in  the  hams,  as  an  unfavorable  medium  or  soil 
would  thus  be  created,  in  which  the  ham-souring  bacillus  could  not 
develop.  The  reason  that  souring  does  develop  in  regular-cure  hams 
is  because  the  pumping  is  not  always  thorough  and  there  are  certain 
areas  in  the  deeper  portions  of  these  hams  which  are  not  saturated 
with  the  pumping  pickle. 

12.  Under  the  present  methods  of  curing,  the  partly  pumped  or 
mild-cure  hams  furnish  the  greater  proportion  of  the  sours,  as  these 
hams  are  not  pumped  in  the  body  and  the  growth  of  the  ham- 
souring  bacillus  within  the  bodies  of  these  hams  is  not  interfered 
with  until  the  curing  pickle  has  penetrated  from  the  outside.  As 
it  requires  several  weeks  for  the  curing  pickle  to  penetrate  thoroughly 
into  the  deeper  portions  of  these  hams,  the  bacillus  is  thus  afforded 
a  considerable  interval  in  which  to  develop. 

13.  The  percentage  of  souring  in  the  mild-cure  hams  could  be 
greatly  reduced  without  materially  affecting  the  cure  by  pumping 
these  hams  with  their  own  curing  pickle,  which  is  usually  a  milder 
pickle  than  that  employed  in  the  regular  cure;  and  if  the  pumping 


ACKNOWLEDGMENTS.  55 

were  thorough  the  number  of  sours  in  these  hams  could  be  reduced 
to  a  small  figure. 

14.  The  only  way  by  which  ham  souring  could  be  entirely  eliminated 
from  the  larger  packing  establishments  under  the  present  methods 
of  curing  would  be  to  handle  the  hams  throughout  under  aseptic 
conditions,  and  this,  for  obvious  reasons,  would  be  an  impossibility. 
The  losses  from  ham  souring  may  be  materially  reduced,  however,  by 
greater  care  in  handling  the  hams  and  the  adoption  of  precautionary 
measures  designed  to  prevent  the  introduction  of  contaminated 
foreign  matter  into  the  bodies  of  the  hams,  together  with  more 
thorough  methods  of  pumping. 

ACKNOWLEDGMENTS. 

In  conclusion,  the  writer  desires  to  express  his  obligations  to  Dr. 
S.  E.  Bennett,  of  the  Inspection  Division,  inspector  in  charge  at 
Chicago,  for  the  assignment  of  trained  meat  inspectors  to  assist  in 
the  work,  as  well  as  for  kind  assistance  in  obtaining  data  and  material 
for  laboratory  study,  and  to  Dr.  L.  E.  Day,  of  the  Pathological 
Division,  who  kindly  prepared  the  sections  which  are  figured  and 
described  in  the  present  article. 

o 


ur 

1  !' 

■iODTH 

-RN  RFGIONAL  LIBRARY  FACILIT 

rriiiiiiiiiiiiiiiiii 

III 

11 

A 

i  III  Illlii 

001 

ii 

iiiiiiiinniii 

137  162 

III 

2 

